Add AnimationTestActivity back

This is a clean cherry-pick from tm-qpr-dev.

I27574365cd3564606cd0e95483d20318cd44ff59 accidentally
removed AnimationTestActivity, which is still used for
AssistantStackTests.

Bug: 266875419
Bug: 267256273
Bug: 234146752
Test: atest android.server.wm.AssistantStackTests#testLaunchIntoSameTask
Change-Id: Ic5943a72e59edfa1e969054f9242decbb378cfdf
Merged-In: Ic5943a72e59edfa1e969054f9242decbb378cfdf
2 files changed