[Flicker tests for bubbles]

1. Add new test as below for bubble notification to detect flicker
2. Remove redual operation in ExpandBubbleScreen.kt
3. Remove assertion from BaseBubbleScreen.kt

Test: 1. atest WMShellFlickerTests:LaunchBubbleFromLockScreen
Bug: 167521723
Change-Id: I6a2d5ce74fcf3aa7861a8ff6c39595fab2149ac2
7 files changed