debugger: First slight pass at UI (#27034)

- Collapse Launch and Attach into a single split button
- Fix code actions indicator being colored red.

Release Notes:

- N/A

crates/ui/src/components/button/split_button.rs

@@ -0,0 +1,45 @@
+use gpui::{
+    div, hsla, point, px, AnyElement, App, BoxShadow, IntoElement, ParentElement, RenderOnce,
+    Styled, Window,
+};
+use theme::ActiveTheme;
+
+use crate::{h_flex, ElevationIndex};
+
+use super::ButtonLike;
+
+/// /// A button with two parts: a primary action on the left and a secondary action on the right.
+///
+/// The left side is a [`ButtonLike`] with the main action, while the right side can contain
+/// any element (typically a dropdown trigger or similar).
+///
+/// The two sections are visually separated by a divider, but presented as a unified control.
+#[derive(IntoElement)]
+pub struct SplitButton {
+    pub left: ButtonLike,
+    pub right: AnyElement,
+}
+
+impl RenderOnce for SplitButton {
+    fn render(self, _window: &mut Window, cx: &mut App) -> impl IntoElement {
+        h_flex()
+            .rounded_sm()
+            .border_1()
+            .border_color(cx.theme().colors().text_muted.alpha(0.12))
+            .child(div().flex_grow().child(self.left))
+            .child(
+                div()
+                    .h_full()
+                    .w_px()
+                    .bg(cx.theme().colors().text_muted.alpha(0.16)),
+            )
+            .child(self.right)
+            .bg(ElevationIndex::Surface.on_elevation_bg(cx))
+            .shadow(smallvec::smallvec![BoxShadow {
+                color: hsla(0.0, 0.0, 0.0, 0.16),
+                offset: point(px(0.), px(1.)),
+                blur_radius: px(0.),
+                spread_radius: px(0.),
+            }])
+    }
+}