[fenix] Define the width/height for homescreen empty collections button (https://github.com/mozilla-mobile/fenix/pull/20082)

app/src/main/res/layout/no_collections_message.xml

@@ -53,6 +53,9 @@
     <com.google.android.material.button.MaterialButton
         android:id="@+id/add_tabs_to_collections_button"
         style="@style/PositiveButton"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:maxLines="2"
         android:layout_marginTop="8dp"
         android:text="@string/tabs_menu_save_to_collection1"
         android:visibility="gone"