dillon1000/react

[Fizz] Postponing in the shell (#27569)

When we postpone a prerender in the shell, we should just leave an empty
prelude and resume from the root. While preserving any options passed
in.

Since we haven't flushed anything we can't assume we've already emitted
html/body tags or any resources tracked in the resumable state. This
introduces a resetResumableState function to reset anything we didn't
flush.

This is a bit hacky. Ideally, we probably shouldn't have tracked it as
already happened until it flushed or something like that.

Basically, it's like restarting the prerender with the same options and
then immediately aborting. When we add the preload headers, we'd track
those as preload() being emitted after the reset and so they get readded
to the resumable state in that case.