Render other tab icons in the start slot (#14683)

This PR reworks the rendering for tab icons to allow us to render all of
the tab icons—not just file icons—in the tab's start slot.

The `Item` trait now has a separate `tab_icon` method that can be used
to indicate what icon should be shown for the tab.

Release Notes:

- N/A

crates/workspace/src/pane.rs

@@ -10,7 +10,6 @@ use crate::{
 };
 use anyhow::Result;
 use collections::{BTreeSet, HashMap, HashSet, VecDeque};
-use file_icons::FileIcons;
 use futures::{stream::FuturesUnordered, StreamExt};
 use gpui::{
     actions, anchored, deferred, impl_actions, prelude::*, Action, AnchorCorner, AnyElement,
@@ -1590,6 +1589,7 @@ impl Pane {
             },
             cx,
         );
+        let icon = item.tab_icon(cx);
         let close_side = &ItemSettings::get_global(cx).close_position;
         let indicator = render_item_indicator(item.boxed_clone(), cx);
         let item_id = item.item_id();
@@ -1597,14 +1597,6 @@ impl Pane {
         let is_last_item = ix == self.items.len() - 1;
         let position_relative_to_active_item = ix.cmp(&self.active_item_index);
 
-        let file_icon = ItemSettings::get_global(cx)
-            .file_icons
-            .then(|| {
-                item.project_path(cx)
-                    .and_then(|path| FileIcons::get_icon(path.path.as_ref(), cx))
-            })
-            .flatten();
-
         let tab = Tab::new(ix)
             .position(if is_first_item {
                 TabPosition::First
@@ -1675,14 +1667,12 @@ impl Pane {
             })
             .map(|tab| match indicator {
                 Some(indicator) => tab.start_slot(indicator),
-                None => tab.start_slot::<Icon>(file_icon.map(|icon| {
-                    Icon::from_path(icon.to_string())
-                        .size(IconSize::XSmall)
-                        .color(if is_active {
-                            Color::Default
-                        } else {
-                            Color::Muted
-                        })
+                None => tab.start_slot::<Icon>(icon.map(|icon| {
+                    icon.size(IconSize::XSmall).color(if is_active {
+                        Color::Default
+                    } else {
+                        Color::Muted
+                    })
                 })),
             })
             .end_slot(