Add inset variant to ListItem (#3422)

This PR adds an inset variant to the `ListItem` component.

We're now using this inset variant for the `ListItem`s we render in
pickers.

Release Notes:

- N/A

crates/command_palette2/src/command_palette.rs

@@ -301,7 +301,7 @@ impl PickerDelegate for CommandPaletteDelegate {
         };
 
         Some(
-            ListItem::new(ix).selected(selected).child(
+            ListItem::new(ix).inset(true).selected(selected).child(
                 h_stack()
                     .justify_between()
                     .child(HighlightedLabel::new(