Avoid repeated allocations in getChildOffsetRelativeToRoot (#55274)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55274

Changelog: [Internal]

Refactors `getChildOffsetRelativeToRoot()` to use a static `Rect` field instead of allocating a new `Rect` and `int[]` on every call. Since this is a private method, we can return the `Rect` directly to avoid the extra `int[]` allocation.

This addresses the code review feedback on D90988373.

Reviewed By: javache

Differential Revision: D91230611

fbshipit-source-id: 64eb23e24f46488075252dafbfbf16a44cf34f67