Scaffold out basic markdown language server (#154293)

* Scaffold out basic markdown lsp

This scaffolds out a new markdown language server and then uses it to implement document symbols. After the change, the markdown extension will have the following structure:

- languageService — Where all the LSP language stuff will eventually land
- server — The actual language server. Consumes ` languageService`
- src — The current extension that launches the server and implements VS Code specific functions

* Adding build scripts

* a

* Use language service from github

* Remove ls build scripts

* Bump versions

* Only build ext

* Enable for web

* Fixing for browser

extensions/markdown-language-features/extension-browser.webpack.config.js

@@ -12,7 +12,7 @@ const withBrowserDefaults = require('../shared.webpack.config').browser;
 module.exports = withBrowserDefaults({
 	context: __dirname,
 	entry: {
-		extension: './src/extension.ts'
+		extension: './src/extension.browser.ts'
 	}
 }, {
 	configFile: 'tsconfig.browser.json'