TimeCheck: Use clock monotonic for elapsed time

The timeout deadline uses clock monotonic.

Update the elapsed time passed to the callbacks to
use clock monotonic as well.  Clock monotonic counts only the
time the CPU is active (vs suspend) and is a better estimate
for performance monitoring.

Test: overnight stress test
Test: atest libmediautils_test
Test: atest timecheck_tests
Bug: 227594853
Merged-In: Ie35de689245a04ba50f4d4f04a10e2e0ded2293b
Change-Id: Ie35de689245a04ba50f4d4f04a10e2e0ded2293b