[Toast] Update A-Z <-> Toast transition for drawable backgrounds.

This and the other change in the topic are protected by a new feature
flag (included here).

Bug: 229297414
Bug: 248006105
Test: manual (see screenshots and recordings in the second bug)
Change-Id: I3478d7e194ee5d3bc4f8affdadbec969c033d084
2 files changed