Publish typings for monaco-typescript TypeScriptWorker

[ecraig12345]

monaco-editor version: 0.17.0
Browser: n/a
OS: n/a

Steps or JS usage snippet reproducing the issue:

I'm working on a browser-based live code editor where we'd like to use various APIs from the TypeScriptWorker, for example getEmitOutput to compile our code--similar to #289.

However, in the typings the API to get the worker returns any, and there's no declaration file generated/published for the TypeScriptWorker file. This makes the worker much less convenient/safe to use.

import * as monaco from 'monaco-editor';

const editor = monaco.editor.create(/*args*/);
const uri = editor.getModel().uri;
// This should have type TypeScriptWorker but actually has type any
const worker = await monaco.languages.typescript.getTypeScriptWorker();
// Now this code isn't type-safe and the API methods aren't discoverable
const workerInstance = await worker(uri);
const result = await workerInstance.getEmitOutput(uri.toString());

We worked around the issue locally by cloning monaco-typescript, building it with declaration: true set in the tsconfig, and copying the declaration files into our project--but it would be much better if the complete typings were included in the published package.

cc: @nishikaza @sopranopillow @kenotron