Adding assertions to ReOpenImeWindowTest

Updating ReOpenImeWindowTest & OpenAppFromOverviewTest transition to wait for fullscreen app instead of hasWindow as this last one was not completely correct.

Adding the assertions for the test ReOpenImeWindowTest.
Adding also some missing assertions to OpenImeWindowTest.

Moving some tests from CommonAssertions launch file to flicker common assertions so that other tests, besides the lunch ones, can use them:
- wallpaperWindowBecomesInvisible
- appLayerReplacesWallpaperLayer

Adding new IME assertions:
- imeWindowBecomesVisible
- imeAppWindowBecomesVisible

Renaming assertion windowAlwaysVisible to appWindowAlwaysVisibleOnTop to be more clear on what it does.

Test: atest FlickerTests
Bug: b/175197807
Change-Id: I157962d53f1254a04c9abef7c6ad2bd1392b1728