Fix CS external dependencies on SystemUI

- Use formal API getSystemService to get ConnectivityManager.
- Use formal API PackageManager#hasSystemFeature(
  PackageManager#FEATURE_TELEPHONY) to know whether device
  supports telephony.
- Use formal API TelephonyManager#isDataCapable() to know
  whether device has mobile ability.
- Replace NetworkCapabilities#equalsTransportTypes with
  comparing two NetworkCapabilities' transport types directly.
- Replace ConnectivityManager#INET_CONDITION_ACTION by listening
  onCapabilitiesChanged() network callback.

Bug: 183068713
Test: atest SystemUITests
Change-Id: I4a53223f36ea09a062a9ddea668a9d0662f0dbbc