[flexiglass] Simplified Dagger setup.

Simplifies the story for how we provide Flexiglass objects through
Dagger and prepares it all for nicer/simpler injection into the
soon-to-be Flexiglass container view.

Bug: 279501596
Test: Built and ran the Compose gallery app with useCompose = false
Test: Built and ran System UI with useCompose = true and useCompose =
false

Change-Id: Ic820caa3067a0fd3a281a4ca68a2af1356276d7b