Send TransitionInfo through onTasksAppeared()

Send the TransitionInfo instance from the recents-merge transition
through onTasksAppeared() to allow Launcher to set the corner radius of
destop tasks to zero during the second part (the post-merge part) of
the recents transition.

Bug: 378657004
Flag: com.android.window.flags.enable_desktop_recents_transitions_corners_bugfix
Test: manual

Change-Id: I92e404f1da2003f2c079067076fe7db52794ccf3