onboarding: Fix onboarding font context menu not scrolling to selected entry open (#36080)

The fix was changing the picker kind we used from `list` variant to a
`uniform` list

`Picker::list()` still has a bug where it's unable to scroll to it's
selected entry when the list is first openned. This is likely caused by
list not knowing the pixel offset of each element it would have to
scroll pass to get to the selected element


Release Notes:

- N/A

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/onboarding/src/editing_page.rs

@@ -573,7 +573,7 @@ fn font_picker(
 ) -> FontPicker {
     let delegate = FontPickerDelegate::new(current_font, on_font_changed, cx);
 
-    Picker::list(delegate, window, cx)
+    Picker::uniform_list(delegate, window, cx)
         .show_scrollbar(true)
         .width(rems_from_px(210.))
         .max_height(Some(rems(20.).into()))