Add the NetworkScanRequestTracker

NetworkScanRequestTracker is part of the new network scan API
implementaion, which stores all the live and pending network scans
and handles the multiplexing of multiple scans.

Test: Telephony sanity tests
Bug: 30954762
Change-Id: I2fd9825f0a5ce3a2fd341cf8d2d9480af81716bd
12 files changed