Send PhoneAccount register/unregistered intents to default dialer.

A few cleanups:
1. When sending the register/unregister phone account intents, previously
there was no attempt made to ensure the intents were only sent when a
new account was added, or an existing one was removed.  Cleaned this up
so that we don't over-send the intents.
2. Minor fix to account diff string in PhoneAccountRegistrar which would
cause icon to always be shown as a diff; removed since bitmaps can't be
compared.
3. Also sending the intents to the default dialer app as an explicit
intent.
Cherry-pick from aosp master to resolve conflicts.

Test: Manual
Bug: 37106957
Change-Id: I7fdaa3e225df6fe3aaf292f9b0b93042f69ca469
diff --git a/testapps/AndroidManifest.xml b/testapps/AndroidManifest.xml
index 6980a12..592145b 100644
--- a/testapps/AndroidManifest.xml
+++ b/testapps/AndroidManifest.xml
@@ -66,7 +66,8 @@
             <intent-filter>
                 <action android:name="android.server.telecom.testapps.ACTION_SEND_UPDATE_REQUEST_FROM_TEST_INCALL_SERVICE"/>
                 <action android:name="android.server.telecom.testapps.ACTION_SEND_UPGRADE_RESPONSE"/>
-                <data android:scheme="int" />
+                <action android:name="android.telecom.action.PHONE_ACCOUNT_REGISTERED"/>
+                <action android:name="android.telecom.action.PHONE_ACCOUNT_UNREGISTERED"/>
             </intent-filter>
         </receiver>