dillon1000/react

Clear finished discrete updates during commit phase (#18515)

* Reproduce a bug where `flushDiscreteUpdates` causes fallback never to be committed

* Ping suspended level when canceling its timer

Make sure the suspended level is marked as pinged so that we return back
to it later, in case the render we're about to start gets aborted.
Generally we only reach this path via a ping, but we shouldn't assume
that will always be the case.

* Clear finished discrete updates during commit phase

If a root is finished at a priority lower than that of the latest pending discrete
updates on it, these updates must have been finished so we can clear them now.
Otherwise, a later call of `flushDiscreteUpdates` would start a new empty render
pass which may cause a scheduled timeout to be cancelled.

* Add TODO

Happened to find this while writing a test. A JSX element comparison
failed because one of them elements had a functional component as an
owner, which should ever happen.

I'll add a regression test later.

Co-authored-by: Andrew Clark <[email protected]>