refactor: Rename json-vscode-extension/ -> vscode-playground

This refactor changes the purpose of the example VSCode extension from
integrating a single language server into VSCode to providing a
playground in which to experiment with the `pygls` framework in
general.

Now the extension will

- Start the server when the user opens the first text file/notebook
- Restart the server if
  - they change Python environment
  - change a setting that affects the client/server
  - trigger it manually via the command palette
  - save the text file containing the current server's source code

Additionally, the following technology upgrades have been performed

- Upgrading `vscode-languageclient-node` to `8.1.0` - adding support
  for the new `v3.17` LSP methods
- Using `@vscode/python-extension` to grab the user's currently
  configured Python environment - rather than forcing them to
  configure it manually.
- Using a `LogOutputChannel` for all client side logging

examples/servers/json_server.py

@@ -360,5 +360,4 @@ def main():
 
 
 if __name__ == "__main__":
-    logging.basicConfig(filename="pygls.log", level=logging.DEBUG, filemode="w")
     main()

examples/vscode-playground/.vscode/launch.json

@@ -0,0 +1,24 @@
+// A launch configuration that compiles the extension and then opens it inside a new window
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch Client",
+            "type": "extensionHost",
+            "request": "launch",
+            "runtimeExecutable": "${execPath}",
+            "args": [
+                "--extensionDevelopmentPath=${workspaceRoot}",
+                "--folder-uri=${workspaceRoot}/../workspace",
+                "--folder-uri=${workspaceRoot}/../servers",
+            ],
+            "outFiles": [
+                "${workspaceRoot}/out/**/*.js"
+            ],
+            // "preLaunchTask": {
+            //     "type": "npm",
+            //     "script": "compile"
+            // },
+        },
+    ],
+}

examples/vscode-playground/README.md

@@ -0,0 +1,47 @@
+# Pygls Playground
+
+This VSCode extension aims to serve two purposes.
+
+- Provide an environment in which you can easily experiment with the pygls framework by trying some of our example servers - or by writing your own
+
+- Provide a minimal example of what it takes to integrate a pygls powered language server into VSCode.
+
+For an example of a more complete VSCode client, including details on how to bundle your Python code with the VSCode extension itself you may also be interested in Microsoft's [template extension for Python tools](https://github.com/microsoft/vscode-python-tools-extension-template).
+
+## Setup
+
+### Install Server Dependencies
+
+Open a terminal in the repository's root directory
+
+1. Create a virtual environment
+   ```
+   python -m venv env
+   ```
+
+1. Install pygls
+   ```
+   python -m pip install -e .
+   ```
+
+### Install Client Dependencies
+
+Open terminal in the same directory as this file and execute following commands:
+
+1. Install node dependencies
+
+   ```
+   npm install
+   ```
+1. Compile the extension
+
+   ```
+   npm run compile
+   ```
+   Alternatively you can run `npm run watch` if you are going to be actively working on the extension itself.
+
+### Run Extension
+
+1. Open this directory in VS Code
+1. Open debug view (`ctrl + shift + D`)
+1. Select `Launch Client` and press `F5`