Create BouncyBall app for testing

Our focused use case is automated testing.

We fork the TouchLatency app code, and substantially strip it down
to just the "bouncy ball" part.  Notably, we entirely remove the
"touch" mode, and remove all interactive UI.

We will likely add some things back in here for various testing modes.
But the focus is on automated testing, so controls will likely be via
Intents or extra string arguments instead of any interactive UI.

Test: Built, installed, and ran
Bug: 408044970
Flag: EXEMPT introducing test app
Change-Id: I6f958ebeb2720acfe8ced70e3d224d99bc68c9b2