(fix/chore) safer wrapper for IIFE grammar plugins

Resolves #3363.

The `rollup` output format changed out from underneath us which
means that our simple text processing of IIFE output broke and
we were outputting invalid JS for our CDN language builds.

Now we wrap the IIFE inside our own second IIFE and then perform
`hljs.registerLanguage` there. This should be more resilient to
future subtle changes in the output.

tools/lib/language.js

@@ -79,15 +79,18 @@ class Language {
 
 
 async function compileLanguage (language, options) {
-  const IIFE_HEADER_REGEX = /^(var hljsGrammar = )?\(function \(\)/;
-
   // TODO: cant we use the source we already have?
   const input = { ...build_config.rollup.browser_iife.input, input: language.path };
   const output = { ...build_config.rollup.browser_iife.output, name: `hljsGrammar`, file: "out.js" };
   output.footer = null;
-  
+
   const data = await rollupCode(input, output);
-  const iife = data.replace(IIFE_HEADER_REGEX, `hljs.registerLanguage('${language.name}', function ()`);
+  const iife = `
+  (function(){
+    ${data}
+    hljs.registerLanguage('${language.name}', hljsGrammar);
+  })();
+  `.trim();
   const esm = `${data};\nexport default hljsGrammar;`;
 
   language.module = iife;