repl: Iterate on design of REPL sessions view (#14987)

This PR iterates on the design of the REPL sessions view.

We now use the same component for both available kernels and running
ones to provide some consistency between the two modes:

<img width="1208" alt="Screenshot 2024-07-22 at 6 49 08 PM"
src="https://github.com/user-attachments/assets/8b5c3600-e438-49fa-8484-cefabf4b44f1">

<img width="1208" alt="Screenshot 2024-07-22 at 6 49 14 PM"
src="https://github.com/user-attachments/assets/5125e9b3-6465-4d1e-9036-e6ca270dedcb">

Release Notes:

- N/A

crates/repl/src/components/kernel_list_item.rs

@@ -0,0 +1,60 @@
+use gpui::AnyElement;
+use ui::{prelude::*, Indicator, ListItem};
+
+use crate::KernelSpecification;
+
+#[derive(IntoElement)]
+pub struct KernelListItem {
+    kernel_specification: KernelSpecification,
+    status_color: Color,
+    buttons: Vec<AnyElement>,
+    children: Vec<AnyElement>,
+}
+
+impl KernelListItem {
+    pub fn new(kernel_specification: KernelSpecification) -> Self {
+        Self {
+            kernel_specification,
+            status_color: Color::Disabled,
+            buttons: Vec::new(),
+            children: Vec::new(),
+        }
+    }
+
+    pub fn status_color(mut self, color: Color) -> Self {
+        self.status_color = color;
+        self
+    }
+
+    pub fn button(mut self, button: impl IntoElement) -> Self {
+        self.buttons.push(button.into_any_element());
+        self
+    }
+
+    pub fn buttons(mut self, buttons: impl IntoIterator<Item = impl IntoElement>) -> Self {
+        self.buttons
+            .extend(buttons.into_iter().map(|button| button.into_any_element()));
+        self
+    }
+}
+
+impl ParentElement for KernelListItem {
+    fn extend(&mut self, elements: impl IntoIterator<Item = AnyElement>) {
+        self.children.extend(elements);
+    }
+}
+
+impl RenderOnce for KernelListItem {
+    fn render(self, _cx: &mut WindowContext) -> impl IntoElement {
+        ListItem::new(SharedString::from(self.kernel_specification.name.clone()))
+            .selectable(false)
+            .start_slot(
+                h_flex()
+                    .size_3()
+                    .justify_center()
+                    .child(Indicator::dot().color(self.status_color)),
+            )
+            .children(self.children)
+            .end_slot(h_flex().gap_2().children(self.buttons))
+    }
+}