Send task description changed though task org taskInfoChanged

- This removes the need for a separate task stack listener and aligns
  with other task info change properties
- Also implement equals/hashCode for the token so we can use it in
  containers

Bug: 148977538
Test: atest TaskOrganizerTests

Signed-off-by: Winson Chung <winsonc@google.com>
Change-Id: Ie035e6389fdbdc374c1a4b4a684758efa0cb7a9e