* chore: vendor Mitt into src/common/third-party
As discussed in #6203 we need to vendor our common dependencies in so
that when we ship an ESM build all imports point to file paths and do
not rely on Node resolution (e.g. a browser does not understand `import
mitt from 'mitt'`).
* chore: enforce file extensions on imports
To make our output agnostic it should include file extensions in the
output, as per the ESM spec. It's a bit odd for Node packages but makes
it easier to publish a browser build.
* chore: remove `installAsyncStackHooks` helper
This code was written when browsers/Node didn't support errors in async
functions very well. They now do a much better job of this, so we can
lose the additonal complexity from our codebase and leave it to the host
environment :)
* lazy launcher is private
* remove async stack test
The headful one I'm permanently skipping as I don't know what the issue is and I can't debug without getting my hands on a Windows machine. If anyone has one or is able to help, that'd be great!
The other I'm deferring another month and will ping the FF folks :)
This CL migrates all the tests to TypeScript. The main benefits of this is that we start consuming our TypeScript definitions and therefore find errors in them. The act of migrating found some bugs in our definitions and now we can be sure to avoid them going forwards.
You'll notice the addition of some `TODO`s in the code; I didn't want this CL to get any bigger than it already is but I intend to follow those up once this lands. It's mostly figuring out how to extend the `expect` types with our `toBeGolden` helpers and some other slight confusions with types that the tests exposed.
Co-authored-by: Mathias Bynens <mathias@qiwi.be>
