dillon1000/react

[Fiber] Adjust the suspensey image/css timeout based on already elapsed time (#34478)

Currently suspensey images doesn't account for how long we've already
been waiting. This means that you can for example wait for 300ms for the
throttle + 500ms for the images. If a Transition takes a while to
complete you can also wait that time + an additional 500ms for the
images.

This tracks the start time of a Transition so that we can count the
timeout starting from when the user interacted or when the last fallback
committed (which is where the 300ms throttle is computed from). Creating
a single timeline.

This also moves the timeout to a central place which I'll use in a
follow up.