Expose NetworkCapabilities methods to system/public APIs

Add methods to system/public APIs for mainline support.

Bug: 139268426
Bug: 135998869
Bug: 138306002
Test: atest FrameworksNetTests
      atest NetworkStackTests
      ./frameworks/opt/net/wifi/tests/wifitests/runtests.sh
      atest FrameworksTelephonyTests
      atest android.net.cts
      atest android.net.wifi.cts
      atest android.telephony.cts

Change-Id: I6ec333309172edaf5aa976f83cfbe63512043594