Add user-visible output for remote operations (#25849)

This PR adds toasts for reporting success and errors from remote git
operations. This PR also adds a focus handle to notifications, in
anticipation of making them keyboard accessible.

Release Notes:

- N/A

---------

Co-authored-by: julia <julia@zed.dev>

crates/diagnostics/src/diagnostics.rs

@@ -995,7 +995,7 @@ fn diagnostic_header_renderer(diagnostic: Diagnostic) -> RenderBlock {
                         h_flex()
                             .gap_1()
                             .child(
-                                StyledText::new(message.clone()).with_highlights(
+                                StyledText::new(message.clone()).with_default_highlights(
                                     &cx.window.text_style(),
                                     code_ranges
                                         .iter()