extensions_ui: Show an error toast when a dev extension fails to install (#22914)

This PR adds an error toast that will be displayed when installing a dev
extension fails.

Here's what it looks like:

<img width="1310" alt="Screenshot 2025-01-09 at 11 56 42 AM"
src="https://github.com/user-attachments/assets/b65eb9f9-c559-4b99-b64a-ee301fa9e443"
/>

<img width="1310" alt="Screenshot 2025-01-09 at 12 10 30 PM"
src="https://github.com/user-attachments/assets/f4880221-2ed9-4bb0-9d48-1cb29c2b483f"
/>

I did have to touch the workspace `ErrorMessagePrompt` component to make
it scroll for long messages. I don't anticipate this being a problem for
other classes of errors (if anything, I suspect other long errors will
become more usable now).

Closes #21237.

Release Notes:

- Added an error toast that is shown when a dev extension fails to
install.

crates/workspace/src/notifications.rs

@@ -392,7 +392,10 @@ impl Render for ErrorMessagePrompt {
                     )
                     .child(
                         div()
+                            .id("error_message")
                             .max_w_80()
+                            .max_h_40()
+                            .overflow_y_scroll()
                             .child(Label::new(self.message.clone()).size(LabelSize::Small)),
                     )
                     .when_some(self.label_and_url_button.clone(), |elm, (label, url)| {