Replaces ThemeSettings builder with updater

Thee new ThemeSettingsUpdater class is independent from ThemeSettings and provides type-safe way to interface with the API without error-prone nullability checkers.

Bug: 333694176
Test: atest FrameworksServicesTests_theme
Flag: android.server.enable_theme_service
Change-Id: I4a4caf10b1b1137e1bb85b588fef633aaa932697