[ Merge of http://go/wvgerrit/93838 ]
Some more rework of policy engine/policy timers code to support
timer and clock value handling introduced by OEMCrypto v16.
Changes are
* renamed methods to include rental duration since policies for v16 use
rental and playback duration for all licenses. Previously rental and
playback durations enforced timing for persistent licenses and license
duration was used for streaming licenses.
* Moved some common code to the base PolicyTimer class from
PolicyTimerV15.
* Corrected data member naming (policy_timers -> policy_timers_)
* Updated comments
Bug: 139372190
Test: Android WV unit/integration tests
Change-Id: Id925ddcc14608a8500f30c2c68486d91608a9abe
68587be8a0