Added StopwatchRule to measure test time

This is a tight test rule only happens in-between Before and After
annotation. It is now dumping test time in millisencods to
instrumentation output.

Bug: 124247942
Test: make PlatformRuleTests; install APK and run test on aosp
cuttlefish device

Change-Id: Ib5d13dcb37c6719084dd6f176cd945c79907db20
Merged-In: Ie7f87563ac346a52ab6ec27f495c8ab52bda14ec