Fix VTS ElapsedRealTime & GetLocationLowPower bugs

 - CR#2716173: Use Qtimer to improve ElapsedRealTimeNanos accuracy
 - CR#2719986: The callbacks could be stale in GnssMeasurement

Bug: 159768476

Test: Ensure VtsHalGnssV2.0/2.1 are all PASS

CRs-fixed: 2716173
CRs-fixed: 2719986
Change-Id: I345e6bbaf67d86b215795a38c4def97cea1b4847
6 files changed