Add cancel compaction reason stats

Which may provide information about throttles that may
be useful to avoid issuing compactions that are being
heavily cancelled in the first place or if a process
is moving in and out of cached state in a lot.

Bug: 233415647
Test: am compact full <package> <uid>

Change-Id: Ied21b4de7d4402f1bc7752c014fb4434f736d2cd