[4/n] Create TaskAppearedListener and TaskInfoChangedListener

The TaskInfoChangedListener and TaskAppearedListener have been
added to allow Listeners to only observer TaskInfo changes for
a given Task without creating a TaskListener which is limited
by the WindowingMode.

Flag: EXEMPT Refactoring
Fix: 417649431
Test: atest WMShellUnitTests:ShellTaskOrganizerTests

Change-Id: I5656f20523170c25b37e01734a0dff887a7f6a98