extensions_ui: Don't block scrolling on disabled extension cards (#22189)

This PR fixes an issue where disabled extension cards would block scroll
events when the mouse was over them.

Instead of using `.occlude`—which captures _all_ mouse events—we use
`.block_mouse_down` to just block mouse down events (to prevent clicking
the buttons on the disabled card). We also set the cursor style to the
default, as it was still switching to the pointer when hovered over top
of one of the buttons.

Release Notes:

- Fixed disabled extensions blocking scroll events in the extensions
list.

crates/extensions_ui/src/components/extension_card.rs

@@ -48,7 +48,8 @@ impl RenderOnce for ExtensionCard {
                             .absolute()
                             .top_0()
                             .left_0()
-                            .occlude()
+                            .block_mouse_down()
+                            .cursor_default()
                             .size_full()
                             .items_center()
                             .justify_center()