Promote stable postsubmit tests to presubmit

Tests were stable in the dashboard for a few days.

Bug: 196213706
Test: atest WMShellFlickerTests:ExpandPipOnDoubleClickTest
Test: atest WMShellFlickerTests:ExitPipWithDismissButtonTest

Change-Id: I0048a75c8330241673a6f8cee4631a6649c88c35
2 files changed