Keep current orientation if the activity doesn't provide orientation

A translucent activity with unspecified orientation won't affect display
orientation (see WindowContainer#getOrientation(int)), so when pre-
computing target rotation (e.g. ActivityRecord#onConfigurationChanged),
it should not consider sensor rotation.

Fix: 434101837
Flag: EXEMPT bugfix
Test: DisplayContentTests#testRotationForActivityInDifferentOrientation
Test: Enable auto rotation. A translucent activity enters pip on a
      fixed portrait activity. Rotate device to landscape. Expand pip.
      The expanded activity should keep portrait appearance.
Change-Id: If951145912180fe53ef06e06911d985e6d0e75be