DO NOT MERGE Let isLocationEnabledForUser() return true location setting

* In API 28, LocationManager#isLocationEnabled() and
  LocationManager#isLocationEnabledForUser(UserHandle) always
  return false when a device has neither LocationManager#GPS_PROVIDER
  nor LocationManager#NETWORK_PROVIDER.
* Instead of letting setLocationEnabled() and isLocationEnabled()
  depend on whether device has GPS or NETWORK location provider, this
  CL changes these two APIs to directly use LOCATION_MODE setting to
  store the location enable state
* Hence when LOCATION_PROVIDERS_ALLOWED contains a provider, the provider
  may be used, but it is not guaranteed to exist
* Settings.java has two workarounds that actually convert:
   - putInt(LOCATION_MODE, LOCATION_MODE_HIGH_ACCURACY)
       => putString(LOCATION_PROVIDERS_ALLOWED, "+gps");
       => putString(LOCATION_PROVIDERS_ALLOWED, "+network");
   - getInt(LOCATION_MODE, LOCATION_MODE_HIGH_ACCURACY)
       => getString(LOCATION_PROVIDERS_ALLOWED):
         - "gps,network" - LOCATION_MODE_HIGH_ACCURACY
         - "gps"         - LOCATION_MODE_SENSORS_ONLY
         - "network"     - LOCATION_MODE_BATTERY_SAVING
	 - others        - LOCATION_MODE_OFF
* Hence this is NOT a new behavior

Bug: 121040693
Bug: 118242060
Bug: 127359153
Test: CTS tests,
android.bluetooth.cts.BluetoothLeScanTest#testBasicBleScan,
android.bluetooth.cts.BluetoothLeScanTest#testScanFilter,
android.location.cts.LocationManagerTest,
android.location2.cts.LocationManagerTest
Change-Id: I7972d8f97f4ca82c58c29641a081ef73fdcb106c