Fix AnimatedPropsRegistry surface-stop resurrection race (#57376)

[bartlomiejbloniarz]

Summary:

AnimatedPropsRegistry::update() runs on the UI thread every animation frame and
created a surface's entry via operator[]. clearOnSurfaceStop() (run on the JS
thread when a surface stops) erases that entry, but an in-flight animation frame
landing after the stop re-created it via operator[] -- and since the surface is
gone, nothing ever cleans it up again. The resurrected entry leaks its
PropsSnapshot and ShadowNodeFamily for the lifetime of the registry.

A surface's entry is legitimately created by getMap(), which
AnimationBackendCommitHook calls on every React commit. stopSurface drains
in-flight commits before unregistering the ShadowTree
(ShadowTreeRegistry::remove takes the registry's unique lock, which excludes the
shared-locked commit visits), so getMap() can never run for a stopped surface.
That leaves update()'s operator[] as the only thing that can resurrect one.

Fix: update() now only refines surfaces that already exist (find instead of
operator[]) and never creates an entry; getMap() remains the sole creator. A
stopped surface can no longer be resurrected, and there is no extra bookkeeping
that could grow over time.

Changelog: [General][Fixed] - Fix a surface-stop race in the C++ Animated shared backend that could permanently leak per-surface animated state

Reviewed By: javache

Differential Revision: D109156094

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@bartlomiejbloniarz has exported this pull request. If you are a Meta employee, you can view the originating Diff in D109156094.

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This pull request has been merged in d9d2502.