Publish extension that makes it easier for users to use TypeScript@next

[mjbvz]

From microsoft/TypeScript#31623

This tracks the VS Code work require to make this happen. Here's the plan:

• Create an extension that includes typescript@next and is auto published every night
  Done - https://github.com/microsoft/vscode-typescript-next
• In VS Code JS/TS support, check to see if this extension is installed and enabled. If it is, use its TS version

This still allows users to use custom global or workspace typescript.tsdk settings, but will replace VS Code's bundled version