fix(language-server): pass correct languageId when creating virtual code

When virtual code was created, the URI was passed as the language ID.
Within MDX this means sometimes no virtual code was created at all,
breaking semantic diagnostics and syntax toggles. The effects may be
different for other implementations.

packages/language-server/lib/project/simpleProject.ts

@@ -21,7 +21,7 @@ export async function createSimpleServerProject(
  const language = createLanguage(languagePlugins, false, uri => {
  const document = server.documents.get(uri);
  if (document) {
- language.scripts.set(uri, document.getSnapshot(), document.uri);
+ language.scripts.set(uri, document.getSnapshot(), document.languageId);
  }
  else {
  language.scripts.delete(uri);