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/server/src/browser/main.ts

@@ -0,0 +1,16 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { BrowserMessageReader, BrowserMessageWriter, createConnection } from 'vscode-languageserver/browser';
+import { startServer } from '../server';
+
+declare let self: any;
+
+const messageReader = new BrowserMessageReader(self);
+const messageWriter = new BrowserMessageWriter(self);
+
+const connection = createConnection(messageReader, messageWriter);
+
+startServer(connection);