ref(js): Improve app boot ordering

[evanpurkhiser]

We don't actually need to wait on initializeMain until after we've completed bootstrapping, which can be done in parallel.

[billyvg]

I think this is slightly harder to read, I would make it a bit more verbose and have some intermediate vars that hold the promises for the import()

  const [bootstrapPromise, initializeMainPromise] = [
    import('app/bootstrap'),
    import('app/bootstrap/initializeMain'),
  ];
  const {bootstrap} = await bootstrapPromise;
  const config = await bootstrap();
  ...

[evanpurkhiser]

good call, I like it

[billyvg]

Suggested change

	// We won't need initalizeMain until we've completedd bootstrap. We can start
	// We won't need initalizeMain until we've completed bootstrap. We can start

[github-actions]

size-limit report

Path	Base Size (493559e)	Current Size	Change
src/sentry/static/sentry/dist/entrypoints/app.js	52.51 KB	52.66 KB	+0.29% 🔺
src/sentry/static/sentry/dist/entrypoints/sentry.css	70.89 KB	70.89 KB	0%