fix(theme): Restore former globalThis.Prism (#10618)

Author: slorber

packages/docusaurus-theme-classic/src/theme/prism-include-languages.ts

@@ -23,6 +23,8 @@ export default function prismIncludeLanguages(
   // avoid polluting global namespace.
   // You can mutate PrismObject: registering plugins, deleting languages... As
   // long as you don't re-assign it
+
+  const PrismBefore = globalThis.Prism;
   globalThis.Prism = PrismObject;
 
   additionalLanguages.forEach((lang) => {
@@ -34,5 +36,9 @@ export default function prismIncludeLanguages(
     require(`prismjs/components/prism-${lang}`);
   });
 
+  // Clean up and eventually restore former globalThis.Prism object (if any)
   delete (globalThis as Optional<typeof globalThis, 'Prism'>).Prism;
+  if (typeof PrismBefore !== 'undefined') {
+    globalThis.Prism = PrismObject;
+  }
 }