Add setting for making the tab's close button always visible (#21352)

Closes https://github.com/zed-industries/zed/issues/20422

<img width="700" alt="Screenshot 2024-11-29 at 22 00 20"
src="https://github.com/user-attachments/assets/4a17d00c-d64f-4b33-97a7-a57766ce6d17">

Release Notes:

- N/A

crates/workspace/src/pane.rs

@@ -1951,7 +1951,9 @@ impl Pane {
         };
 
         let icon = item.tab_icon(cx);
-        let close_side = &ItemSettings::get_global(cx).close_position;
+        let settings = ItemSettings::get_global(cx);
+        let close_side = &settings.close_position;
+        let always_show_close_button = settings.always_show_close_button;
         let indicator = render_item_indicator(item.boxed_clone(), cx);
         let item_id = item.item_id();
         let is_first_item = ix == 0;
@@ -2046,7 +2048,9 @@ impl Pane {
                     end_slot_action = &CloseActiveItem { save_intent: None };
                     end_slot_tooltip_text = "Close Tab";
                     IconButton::new("close tab", IconName::Close)
-                        .visible_on_hover("")
+                        .when(!always_show_close_button, |button| {
+                            button.visible_on_hover("")
+                        })
                         .shape(IconButtonShape::Square)
                         .icon_color(Color::Muted)
                         .size(ButtonSize::None)