Fix orientation change race conditions in IME test

During setup we first launch the activity and then set the orientation
to natural. In most cases this is already the current orientation, so
nothing changes. However if the previous test changed to a different
orientation, this will trigger an activity re-creation. This could be
slightly delayed after the setup, so we might have input_focus and
temporarily lose it during the test, which will fail any IME requests.

This also removes the freezeRotation call, as setting an orientation
also freezes the rotation. Additionally adds a check to restore the
orientation to natural during teardown.

Flag: EXEMPT testfix
Bug: 397765263
Test: atest InputMethodServiceTest
Change-Id: I383bebd027eca7155c55ca0f450589f0255e589e