Allow to use snapshot starting window when launch translucent activity.

There won't create splash screen if the theme of top actiivty is
declared as translucent or floating. But if there already has snapshot
for this task, it should be allowed to choose the snapshot as starting
window while switching this task to top.

Flag: EXEMPT bugfix
Bug: 357208242
Test: launch activity A, while A stop, launch a translucent activity B
in the same task. Launch the app from home again and verify there will
create splash screen.

Change-Id: I1562eef3026aaa2d2c563c0863450f12bb56985f