assistant2: Navigate context strip with keyboard (#23128)

Context pills are now focusable and intractable via the keyboard.

- <kbd>←</kbd> and <kbd>→</kbd> move the focus to the previous or next
item (wrapping if necessary)
- <kbd>↓</kbd> and <kbd>↑</kbd> move the focus vertically
- If the cursor is in the first/last row of the assistant/inline editor,
they will move the focus to the strip
- Inside the strip, they will move the focus to the pill horizontally
overlapping the most
- If already in the first/last row of the strip, they will move to the
first/last pill (like in editors)
- If the first/last pill is focused, they will move the focus back to
the editor
- <kbd>⌫</kbd>  removes the focused pill (unless it's the suggested one)
- <kbd>⏎</kbd> accepts the suggested pill if focused
  


https://github.com/user-attachments/assets/040bc71c-a3ae-4961-9886-2d5c3d290a73



Release Notes:

- N/A

crates/assistant2/src/active_thread.rs

@@ -327,13 +327,11 @@ impl ActiveThread {
                     )
                     .when_some(context, |parent, context| {
                         if !context.is_empty() {
-                            parent.child(
-                                h_flex().flex_wrap().gap_1().px_1p5().pb_1p5().children(
-                                    context.into_iter().map(|context| {
-                                        ContextPill::new_added(context, false, None)
-                                    }),
-                                ),
-                            )
+                            parent.child(h_flex().flex_wrap().gap_1().px_1p5().pb_1p5().children(
+                                context.into_iter().map(|context| {
+                                    ContextPill::new_added(context, false, false, None)
+                                }),
+                            ))
                         } else {
                             parent
                         }