Enable app op history and fix a bug where history was lost.

We are enabling the appop history - brace yourself.

We were computing the last write time based on the last modified
timestamp of the first historical file but since we don't write
files that have no content the first file may not be there. This
change looks up at the timestamp of the history file for the most
recent time inteval.

Also when persisting history we were diving recursively until all
old files are copied to the new state via hard links but failed to
take into account that some files for more recent periods may not
be present as we don't store empty files.

Added some logic to store WTF on disk including stack trace and
historical file names on debuggable builds as this is useful to
track cases where we nuke history due to a bad state.

Test: atest AppOpsTestCases

bug:111061782

Change-Id: I545cc02f82b1cf7e3b28858d69518bd3fbf9f3a0