CTS: Add regression test for getInputMethodWindowVisibleHeight

Adds a test to verify that getInputMethodWindowVisibleHeight can
only be invoked by apps that are currently allowed to interact
with the IME.

Includes the follow-up fix in Ib71f37ce98b901e894d61cdc95cbdcf18c855395.

Bug: 204906124,
Test: atest CtsInputMethodTestCases
Change-Id: Id590ce0d67ccb1eb7a573df64da76f05e8f51865
Merged-In: Id590ce0d67ccb1eb7a573df64da76f05e8f51865