Start launcher behind bubbled task

When converting a task to bubble via app handle menu or drag, start
launcher so it shows up behind the bubbled task.
This is needed in cases where two apps are launched back to back. For
example start Messages and then Calculator from taskbar.
When Calculator is converted to bubble using the app handle menu, it
would start on top of Messages. We need to make sure it starts on top of
Launcher home screen.

Bug: 394651724
Test: atest WMShellUnitTests
Flag: com.android.wm.shell.enable_bubble_to_fullscreen
Change-Id: Idbe1ca9123568613b5e3de579c342d3b67918bda