Handle workspace/didChangeWatchedFiles

This notification is sent unexpectedly by VSCode, observed in #24.

crates/nil/src/server.rs

@@ -230,6 +230,12 @@ impl Server {
                 );
                 Ok(())
             })?
+            .on_sync_mut::<notif::DidChangeWatchedFiles>(|_st, _params| {
+                // Workaround:
+                // > In former implementations clients pushed file events without the server actively asking for it.
+                // Ref: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_didChangeWatchedFiles
+                Ok(())
+            })?
             .finish()
     }