Allow non-resizable apps in split-screen (12/n)

Before, the hint uses PopupWindow to be placed at the bottom right of the
Display, which can't be attached to Task. Now, render size compat button
 hint popup on Task surface with WindowlessWindowManager.

Fix: 178327644
Bug: 176061101
Test: atest WMShellUnitTests:SizeCompatUILayoutTest
Test: atest WMShellUnitTests:SizeCompatHintPopupTest
Change-Id: I6f8d7afc996d7f312516d85deb2bd113eae8bc3f