MediaMetrics: Update service transaction security

Expand trusted uids.
Note calling pid is 0 for one-way transactions.
Move time rounding to WestWorld proto generation so service has better
internal time accuracy.

Test: mediametrics dumpsys, atest mediametrics_tests
Bug: 138583596
Change-Id: I9909e79de34c398bdcfa536c43bb7ea6d43e680b