Add Geocorder.isImplemented()

The Geocorder interface is not part of the Android core.  It
requires a backend service which may or may not be available
on a device.  The new isImplemented static method allows
apps to discover whether the Geocorder is in fact available
on the device.

Change-Id: I2b5cf7bcc9cce4766bcbb156e91edf34b01f9296

services/java/com/android/server/LocationManagerService.java

@@ -1940,6 +1940,10 @@ public class LocationManagerService extends ILocationManager.Stub implements Run
 
     // Geocoder
 
+    public Boolean geocoderIsImplemented() {
+        return mGeocodeProvider != null;
+    }
+
     public String getFromLocation(double latitude, double longitude, int maxResults,
             GeocoderParams params, List<Address> addrs) {
         if (mGeocodeProvider != null) {