Allow LSP adapters to decide, which diagnostics to underline (#31450)

Closes
https://github.com/zed-industries/zed/pull/31355#issuecomment-2910439798

<img width="1728" alt="image"
src="https://github.com/user-attachments/assets/2eaa8e9b-00bc-4e99-ac09-fceb2d932e41"
/>


Release Notes:

- N/A

crates/project/src/lsp_store/clangd_ext.rs

@@ -37,6 +37,15 @@ pub fn is_inactive_region(diag: &Diagnostic) -> bool {
             .is_some_and(|v| v == CLANGD_SERVER_NAME)
 }
 
+pub fn is_lsp_inactive_region(diag: &lsp::Diagnostic) -> bool {
+    diag.severity == Some(INACTIVE_DIAGNOSTIC_SEVERITY)
+        && diag.message == INACTIVE_REGION_MESSAGE
+        && diag
+            .source
+            .as_ref()
+            .is_some_and(|v| v == CLANGD_SERVER_NAME)
+}
+
 pub fn register_notifications(
     lsp_store: WeakEntity<LspStore>,
     language_server: &LanguageServer,