Refactored Shell to use IDumpstateListener.

BugreportProgressService used to poll system properties to get the
progress of the underlying dumpstate process, but now dumpstate provides
a IDumpstateListener and IDumpstateToken binder objects for the same
purpose.

Test: BugreportReceiverTest passes
Test: manual verification

BUG: 31636879

Change-Id: I81d551781a511cb1cc218a27452875b0bb267f7a