dillon1000/react

Temporarily Mount useInsertionEffect while a Gesture snapshot is being computed (#35565)

`useInsertionEffect` is meant to be used to insert `<style>` tags that
affect the layout. It allows precomputing a layout before it mounts.

Since we're not normally firing any effects during the "apply gesture"
phase where we create the clones, it's possible for the target snapshot
to be missing styles. This makes it so that `useInsertionEffect` for a
new tree are mounted before the snapshot is taken and then unmounted
before the animation starts.

Note that because we are mounting a clone of the DOM tree and the
previous DOM tree remains mounted during the snapshot, we can't unmount
any previous insertion effects. This can lead to conflicts but that is
similar to what can happen with conflicts for two mounted Activity
boundaries since insertion effects can remain mounted inside those.

A revealed Activity will have already had their insertion effects fired
while offscreen.

However, one thing this doesn't yet do is handle the case where a
`useInsertionEffect` is *updated* as part of a gesture being applied.
This means it's still possible for it to miss some styles in that case.
The interesting thing there is that since the old state and the new
state will both be applicable to the global DOM in this phase, what
should really happen is that we should mount the new updated state
without unmounting the old state and then unmount the updated state.
Meaning you can have the same hook in the mounted state twice at the
same time.