Allow auto-pip when starting activity with FLAG_ACTIVITY_NO_ANIMATION

FLAG_ACTIVITY_NO_ANIMATION is not intended to disable auto-enter-pip
when launching a new Activity (should use FLAG_ACTIVITY_NO_USER_ACTION
instead).

Bug: 244123029
Test: atest PinnedStackTests
Test: verify no regression on b/222773615
Change-Id: Ibeb0e789f0561c7f701eabe4c9d7ffc8c14afa77