Set up multiple typescript projects

[psrpinto]

(Not opened yet upstream as it depends on element-hq#1056 so must wait for that one to be merged first)

Requires #11

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In the current typescript setup, attempting to use the WebWorker typescript library will not work, as that library is not part of typescript's default libraries. Attempting to require the library through triple-slash directives will result in an error:

// sync-worker.ts

/// <reference lib="WebWorker" />

Definitions of the following identifiers conflict with those in another file:
ImportExportKind, TableKind, ValueType ...

This happens because the WebWorker and DOM (which is part of the default libraries) libs define some of the same types. I consulted with a colleague who has experience with Web Workers in typescript and they recommended using typescript's project references feature to address this issue.

This PR "splits" the codebase into three typescript projects, which share common configuration, but can also have their own configuration to, e.g. import libraries. These projects are:

1. app: Contains all code except workers. Requires the DOM and DOM.iterable libs
2. workers: Contains workers only. Requires the WebWorkers lib. References the app project.
3. sdk: Contains all code except workers. Requires the DOM and DOM.iterable libs. Only emits declarations.

The top-level tsconfig.json only contains references to each project.

Caveats

1. When using project references, the tsc CLI command requires the --build flag. Not passing the --build flag will result in success, but no code has been checked/compiled.
2. Project references require code to be emitted, even if you just want to lint. Compiled files are placed in a .typescript directory.

[ashfame]

No comments from my side as I don't know TypeScript. Sail away ⛵

[psrpinto]

I rebased this on top of integration-sync-worker, thus the force-push, didn't change any code.

[ashfame]

@psrpinto You shouldn't need to rebase your "sync in worker" PRs on integration-sync-worker for creating PRs unless you had a specific reason for doing that.

[psrpinto]

Indeed there was no need to do so, and I won't do it with future PRs. It's just that this branch was created before the integration-sync-worker existed and I wanted to make sure it was based on that branch. In practice nothing changed, except for the commit hashes.

[psrpinto]

This PR was reverted (by force-push) on integration-sync-worker, since it turns out this approach does not fix the issues with workers in typescript we were trying to address.