Fixup button styling (#822)

Author: SUPERCILEX

auth/src/main/res/layout/fui_register_email_layout.xml

@@ -77,7 +77,6 @@
         <Button
             android:id="@+id/button_create"
             style="@style/FirebaseUI.Button"
-            android:layout_gravity="right"
             android:text="@string/fui_button_text_save"
             tools:ignore="RtlHardcoded" />
 

auth/src/main/res/layout/fui_welcome_back_idp_prompt_layout.xml

@@ -23,9 +23,7 @@
 
     <Button
         android:id="@+id/welcome_back_idp_button"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:layout_gravity="end"
+        style="@style/FirebaseUI.Button"
         android:text="@string/fui_sign_in_default" />
 
 </LinearLayout>

auth/src/main/res/values/styles.xml

@@ -101,7 +101,7 @@
     <style name="FirebaseUI.Button" parent="@style/Widget.AppCompat.Button.Colored">
         <item name="android:layout_width">wrap_content</item>
         <item name="android:layout_height">wrap_content</item>
-        <item name="android:layout_gravity">right</item>
+        <item name="android:layout_gravity">end</item>
     </style>
 
     <style name="FirebaseUI.VerifyPhoneButton" parent="FirebaseUI.Button">