Update prompt library styles (#12689)

- Extend Picker to allow passing a custom editor. This allows creating a
custom styled input.
- Updates various picker styles

Before:

![CleanShot 2024-06-05 at 22 08
36@2x](https://github.com/zed-industries/zed/assets/1714999/96bc62c6-839d-405b-b030-31491aab8710)

After:

![CleanShot 2024-06-05 at 22 09
15@2x](https://github.com/zed-industries/zed/assets/1714999/a4938885-e825-4880-955e-f3f47c81e1e3)

Release Notes:

- N/A

crates/picker/src/picker.rs

@@ -103,6 +103,19 @@ pub trait PickerDelegate: Sized + 'static {
         None
     }
 
+    fn render_editor(&self, editor: &View<Editor>, _cx: &mut ViewContext<Picker<Self>>) -> Div {
+        v_flex()
+            .child(
+                h_flex()
+                    .overflow_hidden()
+                    .flex_none()
+                    .h_9()
+                    .px_4()
+                    .child(editor.clone()),
+            )
+            .child(Divider::horizontal())
+    }
+
     fn render_match(
         &self,
         ix: usize,
@@ -552,16 +565,7 @@ impl<D: PickerDelegate> Render for Picker<D> {
             .on_action(cx.listener(Self::use_selected_query))
             .on_action(cx.listener(Self::confirm_input))
             .child(match &self.head {
-                Head::Editor(editor) => v_flex()
-                    .child(
-                        h_flex()
-                            .overflow_hidden()
-                            .flex_none()
-                            .h_9()
-                            .px_4()
-                            .child(editor.clone()),
-                    )
-                    .child(Divider::horizontal()),
+                Head::Editor(editor) => self.delegate.render_editor(&editor.clone(), cx),
                 Head::Empty(empty_head) => div().child(empty_head.clone()),
             })
             .when(self.delegate.match_count() > 0, |el| {