Pinned stack animation: Fix inset logic.

When animating to the fullscreen size, we need
to immediately report insets as if we were fullscreen so that
the app will draw its content in the appropriate aspect ratio
depending on whether or not it plans to paint behind the insets.
Two things were preventing this, first the pinned stack is
skipped for temp task inset calculation, and second we were
passing null as the temp inset bounds.

Bug: 35396882
Test: Move skeleton pinned app to fullscreen. Verify no aspect jump at end.
Change-Id: I670fe9423fbde45d55b95801c6dcbad97b0280d1