[Suspense] Change Suspending and Restarting Heuristics (#15769)

* Track most recent commit time of a fallback globally

This value is going to be used to avoid committing too many fallback
states in quick succession. It doesn't really matter where in the tree
that happened.

This means that we now don't really need the concept of SuspenseState
other than has a flag. It could be made cheaper/simpler.

* Change suspense heuristic

This now eagerly commits non-delayed suspended trees, unless they're
only retries in which case they're throttled to 500ms.

* Restart early if we're going to suspend later

* Use the local variable where appropriate

* Make ReactLazy tests less specific on asserting intermediate states

They're not testing the exact states of the suspense boundaries, only
the result. I keep assertions that they're not already resolved early.

* Adjust Profiler tests to the new heuristics

* Update snapshot tests for user timing tests

I also added a blank initial render to ensuree that we cover the suspended
case.

* Adjust Suspense tests to account for new heuristics

Mostly this just means render the Suspense boundary first so that it
becomes an update instead of initial mount.

* Track whether we have a ping on the currently rendering level

If we get a ping on this level but have not yet suspended, we might
still suspend later. In that case we should still restart.

* Add comment about moving markers

We should add this to throwException so we get these markers earlier.
I've had to rewrite tests that test restarting to account for the delayed
restarting heuristic.

Ideally, we should also be able to restart from within throwException if
we're already ready to restart. Right now we wait until the next yield.

* Add test for restarting during throttled retry

* Add test that we don't restart for initial render

* Add Suspense Heuristics as a comment in Throw