Introduce HydratedActivatable

Setting up an ExclusiveActivatable requires quite a bit of boilerplate
and knowledge about the Hydrator and its activation. This improves the
process by setting it all up in the background and providing convenience
methods that are more in line with Compose methods
`collectAsStateWithLifecycle()`.

Bug: b/416131251
Test: Refactor only verified manually
Flag: com.android.systemui.notification_bundle_ui
Change-Id: I4e9ae510114b7d269dd788fbf26d6b2c106dcf84