Add CTS for registerBestMatchingNetworkCallback

Bug: 188657173
Test: atest CtsNetTestCases:android.net.cts.NetworkAgentTest \
      CtsNetTestCases:android.net.cts.ConnectivityManagerTest
Test: atest CtsNetTestCasesLatestSdk:android.net.cts.NetworkAgentTest \
      CtsNetTestCasesLatestSdk:android.net.cts.ConnectivityManagerTest
      on R device
Merged-In: I81abc1742a3aa965b444d0196f4eaa2393dcad1c
Change-Id: I81abc1742a3aa965b444d0196f4eaa2393dcad1c
  (cherry-picked from aosp/1727824)
2 files changed