feat: Add UI support for PTZ presets (#1920)

- Closes #1889

Whilst a simple change theoretically, the card has such a collection of
surfaces that can overlap other surfaces, it's challenging to get this
to work right! There's a real chance this will have broken something
z-index related (e.g. X overlaps Y when it should not), or (for related
reasons) broken curver corners on the card.

src/scss/submenu.scss

@@ -1,11 +1,10 @@
 @use './button.scss';
+@import './z-index.scss';
 
 :host {
   pointer-events: auto;
-}
 
-mwc-list-item {
-  z-index: 20;
+  --mdc-menu-z-index: #{$z-index-submenu};
 }
 
 ha-icon-button {