Progress reporting improvements

[pepeiborra]

Rework of #1770. Summary of changes:

1. progress reporting logic extracted into its own module
2. Removed one layer of async handling, reducing the chances of race conditions
3. Correctly implement the LSP spec for window/workDoneProgress/create by waiting until the client has responded
4. Fix bugs: division by zero (when todo is 0) and handling when NoProgress
5. Performance: the reporting loop is now O(1) instead of O(N) in the number of files

I think this is the best we can do to close #1749 while sharing the same logic for both tests and app code

[ndmitchell]

I see a few updates to the test - are these fixing race conditions that this patch showed up?

This code is way clearer!

[pepeiborra]

I see a few updates to the test - are these fixing race conditions that this patch showed up?

I fixed a bunch of tests in the previous version of this PR and decided to preserve the fixes. Not necessarily race conditions: often tests rely on sketchy invariants, e.g. a test that waits for three logging notifications before checking if the build session is restarted is going to break for reasons unrelated to the property it's checking.