fix(javascript): add self to BUILT_IN_VARIABLES

Author: Dsaquel

src/languages/lib/ecmascript.js

@@ -157,6 +157,7 @@ export const BUILT_IN_VARIABLES = [
   "localStorage",
   "sessionStorage",
   "module",
+  "self",
   "global" // Node.js
 ];
 

test/markup/javascript/built-in.expect.txt

@@ -1,4 +1,5 @@
 <span class="hljs-keyword">let</span> bi = <span class="hljs-title class_">BigInt</span>(<span class="hljs-string">&#x27;1&#x27;</span>);
 <span class="hljs-keyword">let</span> inf = <span class="hljs-title class_">Infinity</span>
 <span class="hljs-title class_">Number</span>(<span class="hljs-literal">undefined</span>)
-<span class="hljs-keyword">let</span> today = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()
+<span class="hljs-keyword">let</span> today = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()
+<span class="hljs-variable language_">self</span>

test/markup/javascript/built-in.txt

@@ -1,4 +1,6 @@
 let bi = BigInt('1');
 let inf = Infinity
 Number(undefined)
-let today = new Date()
+let today = new Date()
+self
+