Implement an InputHandler trait for gpui2

Co-Authored-By: Marshall <marshall@zed.dev>
Co-Authored-By: Max <max@zed.dev>
Co-Authored-By: Julia <julia@zed.dev>

crates/editor2/src/element.rs

@@ -2623,6 +2623,10 @@ impl Element<Editor> for EditorElement {
             }
         });
 
+        if editor.focus_handle.is_focused(cx) {
+            cx.set_input_handler(editor.handle);
+        }
+
         cx.with_content_mask(ContentMask { bounds }, |cx| {
             let gutter_bounds = Bounds {
                 origin: bounds.origin,