main-window: move bottom switcher to toolbar

The toolbar view is meant for these. This allows
libadwaita's style to apply the way it can be seen in
basically every other GNOME app.

The differences are with the scroll dependent undershoot
instead of an unconditional border.

Signed-off-by: Markus Göllnitz <camelcasenick@bewares.it>
Part-of: <https://gitlab.gnome.org/GNOME/calls/-/merge_requests/791>

src/ui/main-window.ui

@@ -48,16 +48,16 @@
                     <property name="vexpand">True</property>
                   </object>
                 </child>
-                <child>
+              </object>
+            </property>
+          </object>
+        </property>
+        <child type="bottom">
           <object class="AdwViewSwitcherBar" id="switcher_bar">
             <property name="stack">main_stack</property>
           </object>
         </child>
       </object>
-            </property>
-          </object>
-        </property>
-      </object>
     </child>
   </template>