Refactor aws smithy types (#2638)

## Motivation and Context
This PR refactors `aws-smithy-types` crate. 
`Blob`, `Datetime`, `Number` and `Document` structs now goes to it's own
files.
No changes on feature is introduced.

This is a child-PR of #2616 .
However, it is completely independent.

PR that introduces same changes were previously merged to
`unstable-serde` branch, however, it has not been merged to main branch.

## Testing
NA

## Checklist
This PR does not introduce API changes.
----

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copy, and redistribute this contribution, under the terms of your
choice._

rust-runtime/aws-smithy-types/src/blob.rs

@@ -0,0 +1,32 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/// Binary Blob Type
+///
+/// Blobs represent protocol-agnostic binary content.
+#[derive(Debug, PartialEq, Eq, Hash, Clone)]
+pub struct Blob {
+    inner: Vec<u8>,
+}
+
+impl Blob {
+    /// Creates a new blob from the given `input`.
+    pub fn new<T: Into<Vec<u8>>>(input: T) -> Self {
+        Blob {
+            inner: input.into(),
+        }
+    }
+
+    /// Consumes the `Blob` and returns a `Vec<u8>` with its contents.
+    pub fn into_inner(self) -> Vec<u8> {
+        self.inner
+    }
+}
+
+impl AsRef<[u8]> for Blob {
+    fn as_ref(&self) -> &[u8] {
+        &self.inner
+    }
+}

rust-runtime/aws-smithy-types/src/document.rs

@@ -0,0 +1,73 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+use crate::Number;
+use std::collections::HashMap;
+
+/* ANCHOR: document */
+
+/// Document Type
+///
+/// Document types represents protocol-agnostic open content that is accessed like JSON data.
+/// Open content is useful for modeling unstructured data that has no schema, data that can't be
+/// modeled using rigid types, or data that has a schema that evolves outside of the purview of a model.
+/// The serialization format of a document is an implementation detail of a protocol.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Document {
+    /// JSON object
+    Object(HashMap<String, Document>),
+    /// JSON array
+    Array(Vec<Document>),
+    /// JSON number
+    Number(Number),
+    /// JSON string
+    String(String),
+    /// JSON boolean
+    Bool(bool),
+    /// JSON null
+    Null,
+}
+
+impl From<bool> for Document {
+    fn from(value: bool) -> Self {
+        Document::Bool(value)
+    }
+}
+
+impl From<String> for Document {
+    fn from(value: String) -> Self {
+        Document::String(value)
+    }
+}
+
+impl From<Vec<Document>> for Document {
+    fn from(values: Vec<Document>) -> Self {
+        Document::Array(values)
+    }
+}
+
+impl From<HashMap<String, Document>> for Document {
+    fn from(values: HashMap<String, Document>) -> Self {
+        Document::Object(values)
+    }
+}
+
+impl From<u64> for Document {
+    fn from(value: u64) -> Self {
+        Document::Number(Number::PosInt(value))
+    }
+}
+
+impl From<i64> for Document {
+    fn from(value: i64) -> Self {
+        Document::Number(Number::NegInt(value))
+    }
+}
+
+impl From<i32> for Document {
+    fn from(value: i32) -> Self {
+        Document::Number(Number::NegInt(value as i64))
+    }
+}