1/ Integrate legacySplitScreen Flicker tests into individual assertions

1) Integrate companion object inheritance and the default test runner
2) Move launch activity to setup: avoid noise of splash screen
3) Move setRotate() to setup: avoid noise of system windows
   (LetterBox, NavBar, StatusBar...) visibility changes
4) Reducing test time of each test case: remove redundant transition
5) Remve redundant val for readibility
6) Remove navBarLayerIsAlwaysVisible assertion from split test
   the rotation flow of enter split screen :
   Overview(land) -> enter split(portrait) -> split mode(land)
7) Partially enable ROTATION_90 tests
8) Bypass visibleLayersShownMoreThanOneConsecutiveEntry assertion
   for flaky reasons(Splash Screen, LetterBox, BackGestureSurface)

Test: atest WMShellFlickerTests
Bug: 176134495
Bug: 178685668
Bug: 178447631
Change-Id: I1d6153b987e5913a5d9a1fa5b72b9341b40db6fc