Move ViewTransitions helpers to ReactFiberCommitViewTransitions (facebook#32462)

This doesn't change anything. It just moves some functions.

This moves the view transitions helper functions into its own file. This
is similar to how I already moved ReactFiberCommitEffects and
ReactFiberCommitHostEffects out of ReactFiberCommitWork.

This makes it a bit easier to navigate and get an overview of
ReactFiberCommitWork but another motivation is also so that I can refer
to these helpers from
[ReactFiberApplyGesture](https://github.com/facebook/react/pull/32451/files#diff-42297cf327dee8e01d83c85314b8965953b9674e7c4615ce6c430464dcc8550b).

Author: sebmarkbage