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

crates/ui/src/components/icon.rs

@@ -284,6 +284,7 @@ pub enum IconName {
     Update,
     UserGroup,
     Visible,
+    Wand,
     Warning,
     WholeWord,
     XCircle,