(DOCSP-39501): Consolidate Quick Start page (#3280)

## Pull Request Info - SDK Docs Consolidation

Jira ticket: https://jira.mongodb.org/browse/DOCSP-39501

*Staged Page*

- [Quick
Start](https://preview-mongodbdacharyc.gatsbyjs.io/realm/DOCSP-39501/sdk/quick-start/)
- [SwiftUI Quick
Start](https://preview-mongodbdacharyc.gatsbyjs.io/realm/DOCSP-39501/frameworks/swiftui/quick-start/):
Existing content ported over with Realm naming and ref updates
- [Flutter Quick
Start](https://preview-mongodbdacharyc.gatsbyjs.io/realm/DOCSP-39501/frameworks/flutter/quick-start/):
Move existing Flutter-specific content out of quick start to this
relevant section
- [Unity Quick
Start](https://preview-mongodbdacharyc.gatsbyjs.io/realm/DOCSP-39501/platforms/unity/):
Existing content ported over with Realm naming and ref updates

Adding a note here to capture this in the PR record:
- Product has made the call to remove Java SDK info from our "getting
started" content (here and the Install page), so I've removed the Java
and Kotlin (Java SDK) examples from the consolidated quick start page.
- Based on relatively low usage of the Java SDK Quick Start with
LiveData page, and the need to update it to show Kotlin SDK or at the
very least not Partition-Based Sync, I've checked with engineering and
product and am removing this page from the docs. It doesn't seem
worthwhile to continue to incur the maintenance cost.

*Page Source*

Add links to every SDK's pages where you got the SDK-specific
information:

- [C++ Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/cpp/quick-start/)
- [Flutter Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/flutter/quick-start/)
- [Flutter Install
Page](https://www.mongodb.com/docs/atlas/device-sdks/sdk/flutter/install/)
- [Java Local Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/java/quick-starts/quick-start-local/)
- [Java Sync Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/java/quick-starts/quick-start-sync/)
- [Java Quick Start with Live
Data](https://www.mongodb.com/docs/atlas/device-sdks/sdk/java/quick-starts/livedata/)
- [Kotlin Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/kotlin/quick-start/)
- [.NET Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/dotnet/quick-start/)
- [.NET SDK/Quick Start for
Unity](https://www.mongodb.com/docs/atlas/device-sdks/sdk/dotnet/unity/)
- [Node.js Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/node/quick-start/)
- [Swift Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/swift/quick-start/)
- [SwiftUI Quick
Start](https://www.mongodb.com/docs/atlas/device-sdks/sdk/swift/swiftui-tutorial/)

### PR Author Checklist

Before requesting a review for your PR, please check these items:

- [x] Open the PR against the `feature-consolidated-sdk-docs` branch
instead of `master`
- [x] Tag the consolidated page for:
  - genre
  - meta.keywords
  - meta.description

#### Naming
- [x] Update Realm naming and the language around persistence
layer/local/device per [this
document](https://docs.google.com/document/d/126OczVxBWAwZ4P5ZsSM29WI3REvONEr1ald-mAwPtyQ/edit?usp=sharing)
- [x] Include `.rst` files comply with [the naming
guidelines](https://docs.google.com/document/d/1h8cr66zoEVeXytVfvDxlCSsUS5IZwvUQvfSCEXNMpek/edit#heading=h.ulh8b5f2hu9)

#### Links and Refs
- [x] Create new consolidated SDK ref targets starting with "_sdks-" for
relevant sections
- [x] Remove or update any SDK-specific refs to use the new consolidated
SDK ref targets
- [x] [Update any Kotlin API
links](https://jira.mongodb.org/browse/DOCSP-32519) to use the new
Kotlin SDK roles

#### Content
- [x] Shared code boxes have snippets or placeholders for all 9
languages
- [x] API description sections have API details or a generic placeholder
for all 9 languages
- [x] Check related pages for relevant content to include
- [x] Create a ticket for missing examples in each relevant SDK:
Consolidation Gaps epic

### Reviewer Checklist

As a reviewer, please check these items:

- [ ] Shared code example boxes contain language-specific snippets or
placeholders for every language
- [ ] API reference details contain working API reference links or
generic content
- [ ] Realm naming/language has been updated
- [ ] All relevant content from individual SDK pages is present on the
consolidated page

---------

Co-authored-by: cbullinger <[email protected]>

source/frameworks/flutter.txt

@@ -4,11 +4,7 @@
 Build with Flutter
 ==================
 
-.. contents:: On this page
-   :local:
-   :backlinks: none
-   :depth: 2
-   :class: singlecol
+.. toctree::
+   :titlesonly:
 
-Placeholder page for information about building with Flutter. (This may
-be a directory depending on how much content we have/need.)
+   Quick Start </frameworks/flutter/quick-start>

source/frameworks/flutter/quick-start.txt

@@ -0,0 +1,110 @@
+.. _frameworks-flutter-quick-start:
+
+========================
+Quick Start with Flutter
+========================
+
+.. meta:: 
+   :description: Get started using Atlas Device SDK with Flutter in a Flutter application. 
+   :keywords: Realm, Flutter, Flutter SDK, code example
+
+.. facet::
+  :name: genre
+  :values: tutorial
+
+.. facet::
+   :name: programming_language
+   :values: dart
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+This quick start demonstrates how to use Atlas Device SDK with Flutter in a 
+Flutter application. 
+
+.. tip:: Flutter Project or Standalone Dart Project?
+
+   This quick start contains information for using the SDK in a Flutter
+   project. The package that you import and the way you create object
+   models differs when using the SDK in a standalone Dart project. For
+   a quick start using a standalone Dart project, refer to
+   :ref:`sdks-quick-start`.
+
+Install the SDK
+---------------
+
+Install the ``realm`` package for use in Flutter applications. For more
+information about installing the SDK in a Flutter project, refer to 
+:ref:`sdks-install`.
+
+Import the SDK
+--------------
+
+Import the ``realm`` package into any files where you use it.
+
+.. code-block:: dart
+   :caption: ExampleFile.dart
+
+   import 'package:realm/realm.dart';
+
+Define Your Object Model
+------------------------
+
+Your application's **data model** defines the structure of data stored within
+the database. You can define your application's data model via Dart
+classes in your application code with an SDK object schema.
+You then have to generate the :flutter-sdk:`RealmObjectBase <realm/RealmObjectBase-mixin.html>`
+class that's used within your application.
+
+For more information, refer to :ref:`Define an Object Schema 
+<sdks-define-object-schema>`.
+
+.. procedure::
+
+   .. step:: Create a Model Class
+
+      Add an SDK model class. Give your class a private name
+      (starting with ``_``), such as a file ``car.dart`` with a class
+      ``_Car``.
+
+      .. literalinclude:: /examples/generated/flutter/car.snippet.define-model-flutter.dart
+         :language: dart
+         :caption: car.dart
+
+   .. step:: Generate an SDK Object Class
+
+      Generate a RealmObject class ``Car`` from the data model class ``_Car``:
+
+      .. code-block::
+
+         dart run realm generate
+
+      Running this creates a ``Car`` class in a ``car.realm.dart`` file
+      located in the directory where you defined the model class. This ``Car``
+      class is public and part of the same library as the ``_Car`` data model
+      class. The generated ``Car`` class is what's used throughout your
+      application.
+
+   .. step:: Watch for Changes to the Model (Optional)
+
+      You can watch your data model class to generate a new ``Car`` class
+      whenever there's a change to ``_Car``:
+
+      .. code-block::
+
+         dart run realm generate --watch
+
+Perform CRUD Operations and More
+--------------------------------
+
+Installing the library and the commands to generate the models are specific
+to using the SDK with a Flutter project or a standalone Dart project. But
+all the other operations, from reading and writing data to syncing data across
+devices, are the same for a Flutter or standalone Dart project.
+
+To learn more about performing these operations, refer to the main Quick Start. 
+Shared content starts with the :ref:`Open a Database <sdks-quick-start-open-database>`
+section.

source/frameworks/swiftui.txt

@@ -4,12 +4,7 @@
 Build with SwiftUI
 ==================
 
-.. contents:: On this page
-   :local:
-   :backlinks: none
-   :depth: 2
-   :class: singlecol
+.. toctree::
+   :titlesonly:
 
-Placeholder page for information about building with SwiftUI.
-
-This will be a directory with SwiftUI content.
+   Quick Start </frameworks/swiftui/quick-start>