Fix PhoneAuthProvider not using specified FirebaseApp (#803)

Author: SUPERCILEX

auth/src/main/java/com/firebase/ui/auth/ui/phone/PhoneVerificationActivity.java

@@ -230,7 +230,7 @@ private void sendCode(String phoneNumber, boolean forceResend) {
         mPhoneNumber = phoneNumber;
         mVerificationState = VerificationState.VERIFICATION_STARTED;
 
-        getAuthHelper().getPhoneAuthProviderInstance().verifyPhoneNumber(
+        getAuthHelper().getPhoneAuthProvider().verifyPhoneNumber(
                 phoneNumber,
                 AUTO_RETRIEVAL_TIMEOUT_MILLIS,
                 TimeUnit.MILLISECONDS,

auth/src/main/java/com/firebase/ui/auth/util/AuthHelper.java

@@ -40,7 +40,7 @@ public SaveSmartLock getSaveSmartLockInstance(HelperActivityBase activity) {
         return SaveSmartLock.getInstance(activity);
     }
 
-    public PhoneAuthProvider getPhoneAuthProviderInstance() {
-        return PhoneAuthProvider.getInstance();
+    public PhoneAuthProvider getPhoneAuthProvider() {
+        return PhoneAuthProvider.getInstance(getFirebaseAuth());
     }
 }

auth/src/test/java/com/firebase/ui/auth/testhelpers/AuthHelperShadow.java

@@ -67,7 +67,7 @@ public static SaveSmartLock getSaveSmartLockInstance(HelperActivityBase activity
     }
 
     @Implementation
-    public static PhoneAuthProvider getPhoneAuthProviderInstance() {
+    public static PhoneAuthProvider getPhoneAuthProvider() {
         return sPhoneAuthProvider;
     }