Do not capture activity snapshot if starting window is associated to task.

There doesn't need to capture snapshot from an activity if the starting
window is associated to task, everything should be hide behide the
window.

Bug: 290319270
Test: atest TransitionTests SyncEngineTests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2bb3be0276646895a92d6107bf83c3976e8aa022)
Merged-In: I78eda58c3ec8405498b3c32ecc66b3d529cdb38c
Change-Id: I78eda58c3ec8405498b3c32ecc66b3d529cdb38c