[Feature Request] [Messages GUI] Phone speaker mode toggle

Would be neat to be able to toggle the phones (Android in my case) speaker calling mode from the watch screen when answering a call from the wrist. So a button in the UI for doing that is what I suggest.

Start by locating the Messages GUI app and its call-answer screen, then trace how the watch communicates the call action to the Android phone. Confirm how a speaker-mode toggle can be represented and test it while answering a call. Done means the watch UI exposes the toggle and it changes the phone's speaker calling mode.

Written by the indexing model from the issue text.