Add ConnectivityManager.networkCapabilitiesForType()

This static method returns a NetworkCapabilities instance with
transports and capabilities set according to the given legacy type.

Also:
    - add NetworkRequest.Builder.setCapabilities(), to be able to use
      the NetworkCapabilities instances returned from the above
    - update UpstreamNetworkMonitor to make immediate use of this

Test: as follows
    - build (bullhead)
    - flashed
    - booted
    - runtest frameworks-net passes
    - WiFi to DUN upstream tethering works
Bug: 32163131

Change-Id: Idfe1ddd2815c355cbf27cf29eb0e3de177de84e9