Move ImsResolver to a singleton pattern

In order for dependencies in frameworks/opt/telephony to be
able to access ImsResolver, move ImsResolver to a singleton
pattern.

Bug: 188208808
Test: atest TeleServiceTests
Change-Id: I424461bfc7b2472193a023c85b760b5195421d42
diff --git a/src/com/android/phone/ImsRcsController.java b/src/com/android/phone/ImsRcsController.java
index bcc312c..90c9df4 100644
--- a/src/com/android/phone/ImsRcsController.java
+++ b/src/com/android/phone/ImsRcsController.java
@@ -94,7 +94,7 @@
         mApp = app;
         TelephonyFrameworkInitializer
                 .getTelephonyServiceManager().getTelephonyImsServiceRegisterer().register(this);
-        mImsResolver = mApp.getImsResolver();
+        mImsResolver = ImsResolver.getInstance();
     }
 
     /**