Remove ImeFlickerTests button tap dependency

This fixes some flakes in ImeFlickerTests where the buttons that needed
to be tapped during the test runs were covered by the IME (either due to
small display size, or floating keyboard mode in landscape).

Instead, we use a BroadcastReceiver and create custom intent actions for
the required behaviours.

Test: atest FlickerTestsIme2:OpenImeWindowToFixedPortraitAppTest -- --module-arg FlickerTestsIme2:include-annotation:android.platform.test.annotations.Presubmit --module-arg FlickerTestsIme2:exclude-annotation:android.platform.test.annotations.IwTest
Bug: 310868933
Change-Id: I44baf01a0c5cbfd1f0e51be09075de0a3c7ea967