Add GnssPowerStats Metrics

Adding energy consumption values metrics. These report different levels
of GNSS functionality to get a better understanding of GNSS energy usage.

Design doc: http://doc/1tgHcXFH2hF50PZyJopSwcO5aDC2yCSlqhBmAyThcMJk

Bug: 174181772
Test: atest GnssPowerStatsTests
Change-Id: I73183b5a89e66c314c3884177e9115c507e9dc96