API to expose debugger command to other extensions

[DonJayamanne]

Requirements:

• Determine when extension is ready to use by user
• Determine when extension is ready to use LS functionality.
  • E.g. IntelliCode needs to know LS has started.
  • Make use of existing API (nothing new will be added)
• Provide method to return part of the debug launcher command for remote debugging
  • Azure Functions App
• Document this API
  • On some readme doc in repo
  • On VSCode Docs?
• Create function tests to ensure APIs work as expected

Here's the current API we return:

interface IExtensionApi {
	ready: Promise<void>;
}

const extension = vscode.extensions.getExtension<IExtensionApi>('ms-python.python');

Here's the proposed API:

interface IExtensionApi {
	ready: Promise<void>;  // **Everything** is ready in the extension.
	debug: {
		/** 
		 * Generate an array of strings for commands to pass to the Python executable to launch the debugger for remote debugging.
		 * Users can append another array of strings of what they want to execute along with relevant arguments to Python. 
		 * E.g `['/Users/..../pythonVSCode/pythonFiles/experimental/ptvsd_launcher.py', '--host', 'localhost', '--port', '57039', '--wait']`
		*/
		getRemoteLauncherCommand(host:string, port: number, waitUntilDebuggerAttaches:boolean = true): Promise<string[]>
	}
}

[vivlimmsft]

It would be handy to provide the LS version to extenders as well. Then IntelliCode can do a runtime check on the version of LS and gracefully show a notification if there is a mismatch.

[brettcannon]

@vivlimmsft we are currently planning to pin to the language server version for each release once the language server goes stable, so an API for that shouldn't be necessary short/medium-term.