Introduce GameSession.onTransientSystemBarsVisibilityFromRevealGestureChanged(...)

Adds support for a GameSession to detect when the transient system bars
are revealed and hidden using the GameSession reveal gesture.

Test: Manual e2e testing
Bug: 210119966
Bug: 202414447
Bug: 202417255
CTS-Coverage-Bug: 206128693
Change-Id: I614f9aeae65d6be6e3262ef58011612062036b35