Check finishing opaque activity for closing TaskFragment

Before, when the TaskFragment and its children Activity is finishing
together, we always consider the TaskFragment as translucent.

Now, when the TaskFragment is closing, we also check if there is any
finishing Activity that is opaque.

Fix: 268433205
Test: atest WmTests:TransitionTests
Change-Id: I6ebeb2713aeb64717e53fb2c507dfb11611e4ec5