Add mTimeStamp to SignalStrength

Add mTimestamp since boot in nanoseconds to SignalStrength.
Add a public API getTimestampNanos() in Signal Strength.
Add a public API getTimestampNanos() in CellInfo.
Deprecate public API getTimeStamp() in CellInfo.

Bug: 147157937
Test: atest  SignalStrengthTest (unit and CTS)
Change-Id: I478284a983bb3b5e33b7e0e50362a3aeddbc8545
3 files changed