Fix aspect ratio for transparent letterboxed activity

Set the `OpenTransparentActivity` to have a min aspect ratio to ensure
the activity is always letterboxed in all orientations.

Flag: NONE(bug fix)
Fixes: 371124711
Fixes: 371125446
Test: atest WMShellFlickerTestsAppCompat:OpenTransparentActivityTest

Change-Id: Id3254a1395e40cd9003d7026da7eb324be01ef4a