status/power: Merge with system indicator

Now that the old system menu has been ported over, we can move
the power toggle to its intended place. The main difference to
the stand-alone toggle is that the button now uses its natural
size rather than the fixed size of regular quick items.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2393>

data/theme/gnome-shell-sass/widgets/_quick-settings.scss

@@ -86,4 +86,14 @@
 
 .quick-settings-system-item {
   & > StBoxLayout { spacing: 2 * $base_padding; }
+
+  & .power-item {
+    min-height: 0;
+    min-width: 0;
+
+    &:insensitive {
+      @include button(normal);
+      background-color: transparent;
+    }
+  }
 }