dillon1000/react

Mount/unmount passive effects when Offscreen visibility changes (#24977)

* Remove unnecessary try-catch from passive deletion

The individual unmount calls are already wrapped in a catch block, so
this outer one serves no purpose.

* Extract passive unmount effects to separate functions
    
I'm about to add a "disconnect passive effects" function that will share
much of the same code as commitPassiveUnmountOnFiber. To minimize the
duplicated code, I've extracted the shared parts into separate
functions, similar to what I did for commitLayoutEffectOnFiber and
reappearLayoutEffects.

This may not save much on code size because Closure will likely inline
some of it, anyway, but it makes it harder for the two paths to
accidentally diverge.

* Mount/unmount passive effects on hide/show

This changes the behavior of Offscreen so that passive effects are
unmounted when the tree is hidden, and re-mounted when the tree is
revealed again. This is already how layout effects worked.

In the future we will likely add an option or heuristic to only unmount
the effects of a hidden tree after a delay. That way if the tree quickly
switches back to visible, we can skip toggling the effects entirely.

This change does not apply to suspended trees, which happen to use
the Offscreen fiber type as an implementation detail. Passive effects
remain mounted while the tree is suspended, for the reason described
above — it's likely that the suspended tree will resolve and switch
back to visible within a short time span.

At a high level, what this capability enables is a feature we refer to
as "resuable state". The real value proposition here isn't so much the
behavior of effects — it's that you can switch back to a previously
rendered tree without losing the state of the UI.

* Add more coverage for nested Offscreen cases