Add basebandCn0Dbhz to GnssMeasurement

The new basebandCn0DbHz is the carrier-to-noise density measured at the
baseband. The old Cn0DbHz is measured at the attenna port. Adding
the new field so that ecosystem will report both and avoid reporting
inconsistent signal strengths in one field. See go/r-gnss-hal for
detailed design.

Bug: 136136192
Test: atest GnssMeasurementTest
Change-Id: Ia8d3711e7422db5cae05d66138a3fae61bec0ae1