Add callback to notify frozen RecentTasks

TaskStackListener can now know when
RecentTasks recents list has been
frozen and unfrozen.
Launcher needs this to know when to listen
for multiple swipe regions in quickstep
for apps with different orientations.

Fixes: 140116135
Test: Had Launcher be a consumer of new
listener and verified via logs and
debugger that it was sending the correct
callback when quickswitching apps.

Change-Id: I65fb92d2490c91837523b99563d4fef422dabb76