Set Wi-Fi dialog spinners to 48dps tall

Set the minimum height to align with the accessibility guidelines
and to disable ripple projection.

Also adds scroll indicators to the scroll view.

Bug: 28683023
Change-Id: I24c58c0d6e8ef4b9efc8b3f877bcd659f42b6c6d

res/values/styles.xml

@@ -228,6 +228,10 @@
         <item name="android:textColor">?android:attr/textColorPrimary</item>
     </style>
 
+    <style name="wifi_item_spinner" parent="wifi_item_content">
+        <item name="android:minHeight">48dp</item>
+    </style>
+
     <style name="wifi_advanced_toggle" parent="wifi_item_content">
         <item name="android:background">@null</item>
         <item name="android:button">@null</item>