[Menu][A11y] Make context menu TextView focusable on Menu demo screen

This allows keyboard users to navigate to the TextView and trigger the context menu using the keyboard, improving accessibility within the demo.

PiperOrigin-RevId: 800382654

Author: Material Design Team

catalog/java/io/material/catalog/menu/res/layout/cat_menu_fragment.xml

@@ -104,6 +104,7 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:padding="16dp"
+        android:focusable="true"
         android:text="@string/menu_context_menu_description"/>
 
   </LinearLayout>

catalog/java/io/material/catalog/menu/res/values/strings.xml

@@ -31,7 +31,7 @@
   </string>
 
   <string name="menu_context_menu_description" description="Text explaining how to use context menus [CHAR_LIMIT=NONE].">
-    This TextView opens a context menu when long pressed.
+    This TextView opens a context menu when long pressed or by pressing Enter on a keyboard.
     \n\nIt provides actions that affect the selected content or context frame.
   </string>
   <string name="context_menu_highlight" description="text for a menu option to highlight text [CHAR_LIMIT=20].">Highlight</string>