Implement Gnss::start() and Gnss::stop()

- calling start() creates a thread that periodically receives locations

Bug: 73845705

Test: ran VtsHalGnssV1_1TargetTest. SetCallbackResponses and
GetLocationLowPower are passing

Change-Id: I6a544c2832037a8b507c0ab030a8b766be499669
4 files changed