Support diagnostic navigation in multibuffers (#22620)

cc @nathansobo 

Release Notes:

- Support diagnostic navigation in multibuffers

crates/diagnostics/src/items.rs

@@ -1,11 +1,11 @@
 use std::time::Duration;
 
-use editor::Editor;
+use editor::{AnchorRangeExt, Editor};
 use gpui::{
     EventEmitter, IntoElement, ParentElement, Render, Styled, Subscription, Task, View,
     ViewContext, WeakView,
 };
-use language::Diagnostic;
+use language::{Diagnostic, DiagnosticEntry};
 use ui::{h_flex, prelude::*, Button, ButtonLike, Color, Icon, IconName, Label, Tooltip};
 use workspace::{item::ItemHandle, StatusItemView, ToolbarItemEvent, Workspace};
 
@@ -148,7 +148,11 @@ impl DiagnosticIndicator {
             (buffer, cursor_position)
         });
         let new_diagnostic = buffer
-            .diagnostics_in_range::<_, usize>(cursor_position..cursor_position, false)
+            .diagnostics_in_range(cursor_position..cursor_position, false)
+            .map(|DiagnosticEntry { diagnostic, range }| DiagnosticEntry {
+                diagnostic,
+                range: range.to_offset(&buffer),
+            })
             .filter(|entry| !entry.range.is_empty())
             .min_by_key(|entry| (entry.diagnostic.severity, entry.range.len()))
             .map(|entry| entry.diagnostic);