Adjust design of the slash command picker (#19973)

This PR removes the quote selection icon button from the footer and adds
it in the picker, and adds an icon field to each command entry. Final
result looks like:


https://github.com/user-attachments/assets/d177f1c1-b6f6-4652-9434-f6291b279e34

Release Notes:

- N/A

assets/icons/wand.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-wand"><path d="M15 4V2"/><path d="M15 16v-2"/><path d="M8 9h2"/><path d="M20 9h2"/><path d="M17.8 11.8 19 13"/><path d="M15 9h.01"/><path d="M17.8 6.2 19 5"/><path d="m3 21 9-9"/><path d="M12.2 6.2 11 5"/></svg>