[native] Convert ComposedMessage into a functional component

Summary:
This allows us to memoize things in a more precise way and reduces some re-renders of child components.

Depends on D9051

Test Plan: ComposedMessage continues to behave as expected. A little more "gray" in the flamegraph (components aren't re-rendering), but nothing super impactful. Hopefully there will be more significant improvements in conjunction w/ subsequent diffs.

Reviewers: ginsu, rohan, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9052