3-button mode tests for IME tests

Tests now run in:
  - Portrait + 3 Button
  - Landscape + 3 Button
  - Portrait + Gestural
  - Landscape + Gestural

Test: atest FlickerTests:com.android.server.wm.flicker.ime
Bug: 167521849
Change-Id: Ib7deb76b0c9b6db9a812c615dec6223b50223c18