3/ Add wmHelper to controll the state of test activity

* launchSplitScreen(wmHelper)
* reopenAppFromOverview(wmHelper)
* openQuickstep(wmHelper)
+ waitForActivityDestroyed()

Test: atest FlickerTests
Test: atest WMShellFlickerTests
Test: atest WindowManagerSmokeTest
Bug: 179116910
Change-Id: Ic050a255ebfe5bbe657af7383e5bbe90ca0d56a8