Allow associating the starting window after a trampoline launches.

An app can create a task fragment from a trampoline activity after the
initial launch. If the initial transition has already occurred, the
starting window cannot be associated with the task because the task
will not participate in the follow-up transition. By checking whether
the task's bounds equal the activity's bounds, we can determine if the
currently launched activity is in an adjacent embedded.

This also avoids transferring the starting window between activities of
different sizes, as redrawing it in such cases can look strange.

Bug: 439021625
Flag: EXEMPT bugfix
Test: cold launch with sample app several times and verify no flicker.

Change-Id: I261722cc466f51d8c3557e1dcbeee2800519ddb5