LibJS: Parse arrow function expression with correct precedence

The parser was chomping on commas present after the arrow function expression. eg. [x=>x,2] would parse as [x=>(x,2)] instead of [(x=>x),2].

This is not the case anymore. I've added a small test to prove this.

Libraries/LibJS/Tests/arrow-functions.js

@@ -16,6 +16,10 @@ try {
     };
     assert(addBlock(5, 4) === 9);
 
+    let chompy = [(x) => x, 2];
+    assert(chompy.length === 2);
+    assert(chompy[0](1) === 1); 
+
     const makeObject = (a, b) => ({ a, b });
     const obj = makeObject(33, 44);
     assert(typeof obj === "object");