Add conversations image resource

- Conversations image resource is a compilation of the conversation
icons that are allowed to bypass DND
- Update category header text on DND > Display options for hidden notifications
page
- Update a11y bug in messages and calls pref pages that said images were
tappable

Test: manual
Bug: 151845457
Change-Id: I5387722abf0543b6e07378d498cc0085122c91b9

res/xml/zen_mode_messages_settings.xml

@@ -27,7 +27,8 @@
         <!-- Senders image -->
         <com.android.settingslib.widget.LayoutPreference
             android:key="zen_mode_messages_image"
-            android:layout="@layout/zen_mode_senders_image" />
+            android:layout="@layout/zen_mode_senders_image"
+            android:selectable="false"/>
     </PreferenceCategory>
 
     <com.android.settingslib.widget.FooterPreference/>