Set size compat UI to max layer

Before, the size compat UI is reparent to Task with its original layer
(likely 1), which may not be the higheset layer when the Task contains
more than one children.

Fix: 181541449
Bug: 178327644
Test: verify with launching a non-resizable activity from another
Change-Id: I9e812ca8c0c1fd5b93a6e074a5e4df164c8fa03b