[Fizz] Fix aborts during resumed rendering (#36584)

Stacked on #36583

Fizz previously identified a task that was rendering during an abort by
marking its blocked Segment as `RENDERING`. This does not work for
resumed replay tasks because they do not have a Segment, so an abort
during replay could eagerly abort the task before it unwound and then
report the internal `null` throw instead of the abort reason.

Track the task currently executing on the Request so aborting can leave
the in-flight task to unwind through its normal error path for both
render and replay tasks. Since this replaces the only purpose of the
Segment `RENDERING` status, remove that status and its associated
bookkeeping.

When resumed work unwinds after aborting, use the request's abort reason
in the replay catch paths so aborting while replaying a prerendered tree
or while rendering a resumed segment reports the meaningful abort reason
instead of the internal control-flow value.