* Compiler no longer has its own Tokio runtime. Compiler handles one
  message and then exits.

* Uses the simpler ts.CompilerHost interface instead of
  ts.LanguageServiceHost.

* avoids recompiling the same module by introducing a hacky but simple
  `hashset<string>` that stores the module names that have been already
  compiled.

* Removes the CompilerConfig op.

* Removes a lot of the mocking stuff in compiler.ts like `this._ts`. It
  is not useful as we don't even have tests.

* Turns off checkJs because it causes fmt_test to die with OOM.