[DO NOT MERGE] Expose RRO completion signal

ThemeOverlayController now notifies server when color resources are ready. Now Home and SetupWizard are guaranteed to launch  with proper theming.

In main, this is merged as I0a295e64f1ee5cf27fb1248973c77707e6bcde07.

Test: presubmits
Bug: 307507412
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a329a4f048bc85bf87fa18ffec422183a525643b)
Merged-In: Ifc839aec9fd5b88112218e1d04340a99db4be2c6
Change-Id: Ifc839aec9fd5b88112218e1d04340a99db4be2c6