Fine-tune status bar left-side spacing (#21306)

Closes https://github.com/zed-industries/zed/issues/21291

This PR also adds a small divider separating the panel-opening controls
from the other items that appear on the left side of the status bar. The
spacing was a bit bigger before because all three items on the left open
panels, whereas each other item does different things (e.g., open the
diagnostics tab, update the app, display language server status, etc.).
Therefore, they needed to be separated somehow to communicate the
difference in behavior. Hopefully, now, the border will help sort of
figuring this out.

| With error | Normal state |
|--------|--------|
| <img width="1179" alt="Screenshot 2024-11-28 at 18 52 58"
src="https://github.com/user-attachments/assets/bf4bad19-5588-481a-9d08-91b2227e44e6">
| <img width="1234" alt="Screenshot 2024-11-28 at 18 53 03"
src="https://github.com/user-attachments/assets/4443a16a-9982-44ce-9005-64d4df46f4f0">
|

Release Notes:

- N/A

crates/diagnostics/src/items.rs

@@ -1,7 +1,7 @@
 use editor::Editor;
 use gpui::{
-    rems, EventEmitter, IntoElement, ParentElement, Render, Styled, Subscription, View,
-    ViewContext, WeakView,
+    EventEmitter, IntoElement, ParentElement, Render, Styled, Subscription, View, ViewContext,
+    WeakView,
 };
 use language::Diagnostic;
 use ui::{h_flex, prelude::*, Button, ButtonLike, Color, Icon, IconName, Label, Tooltip};
@@ -77,8 +77,10 @@ impl Render for DiagnosticIndicator {
         };
 
         h_flex()
-            .h(rems(1.375))
             .gap_2()
+            .pl_1()
+            .border_l_1()
+            .border_color(cx.theme().colors().border)
             .child(
                 ButtonLike::new("diagnostic-indicator")
                     .child(diagnostic_indicator)