Misc doc & logging changes

- Update docs to provide guidance for listening for config changes
- Deprecate ShellController config-change path since it only reports app
  config changes (which aren't helpful for multidisplay)
- Add log when starting recents transition to better surface double-start
  scenarios
- Extend logs with merging & finishing remote transitions

Bug: 378565144
Flag: EXEMPT bugfix
Test: atest WMShellUnitTests

Change-Id: I021db99aae156a42079ce26a065a261ff7b2fbcb