Launch Activity by using ActivityScenario instead of ActivityTestRule

Also, wait for the device to be idle after launching an activity

Bug: 335201560
Test: atest AccessibilityDisplayProxyTest --iterations 50
Test: atest AccessibilityEmbeddedHierarchyTest --iterations 50
Flag: TEST_ONLY

Change-Id: I3a75efd38d580be71a5aaf6f2c78013e5ff8b8e5
2 files changed