Fix isVisibleOrAdding and update name/docs

At some point, the functionality drifted from the name and
documentation. This changes the functionality back to the mismatching
functionality, but renames the method and updates the documentation to
match the behavior.

Bug: 205075200
Bug: 205761007
Bug: 204948120
Bug: 204731658
Test: open dev options in settings, click search, observe ime showing
Test: atest OpenImeWindowAndCloseTest
Change-Id: I3ec44ef6c444bbcfa60571ce8e39e3d531af64d7