Merge clangd's inactiveRegions with existing diagnostics (#26737)

Closes: https://github.com/zed-industries/zed/issues/13089

This PR attempts to resolve the issues discussed in my previous PR
#26146.

Release Notes:

- Fixed: `inactiveRegions` doesn't replace existing diagnostics anymore

crates/languages/src/rust.rs

@@ -255,7 +255,12 @@ impl LspAdapter for RustLspAdapter {
         Some("rust-analyzer/flycheck".into())
     }
 
-    fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {
+    fn process_diagnostics(
+        &self,
+        params: &mut lsp::PublishDiagnosticsParams,
+        _: LanguageServerId,
+        _: Option<&'_ Buffer>,
+    ) {
         static REGEX: LazyLock<Regex> =
             LazyLock::new(|| Regex::new(r"(?m)`([^`]+)\n`$").expect("Failed to create REGEX"));
 
@@ -959,7 +964,7 @@ mod tests {
                 },
             ],
         };
-        RustLspAdapter.process_diagnostics(&mut params);
+        RustLspAdapter.process_diagnostics(&mut params, LanguageServerId(0), None);
 
         assert_eq!(params.diagnostics[0].message, "use of moved value `a`");