Assign diagnostics a group_id based on their related_information

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/project/src/worktree.rs

@@ -3633,7 +3633,8 @@ mod tests {
                     Point::new(0, 9)..Point::new(0, 10),
                     &Diagnostic {
                         severity: lsp::DiagnosticSeverity::ERROR,
-                        message: "undefined variable 'A'".to_string()
+                        message: "undefined variable 'A'".to_string(),
+                        group_id: 0,
                     }
                 )]
             )