Add system API to get registered connection managers

This API is used to check if we're in the simplified
version of the call assistant settings UI or the version
that displays a full list.

Bug: 18473946
Change-Id: I7dca50ada80b2203bd8d646bb510418646382df8

telecomm/java/android/telecom/TelecomManager.java

@@ -461,6 +461,16 @@ public class TelecomManager {
         return getSimCallManager();
     }
 
+    /**
+     * Returns the list of registered SIM call managers.
+     * @return List of registered SIM call managers.
+     * @hide
+     */
+    @SystemApi
+    public List<PhoneAccountHandle> getRegisteredConnectionManagers() {
+        return getSimCallManagers();
+    }
+
     /**
      * Returns a list of the {@link PhoneAccountHandle}s which can be used to make and receive phone
      * calls which support the specified URI scheme.