LibJS: Bring Reflect.construct() closer to the specification

This includes checking that the target is a constructor, not just a
function, as well as switching the order of the list creation and
argument validation to match the specification, to ensure correct
exception throwing order.

Userland/Libraries/LibJS/Tests/builtins/Reflect/Reflect.construct.js

@@ -9,7 +9,7 @@ describe("errors", () => {
                 Reflect.construct(value);
             }).toThrowWithMessage(
                 TypeError,
-                "First argument of Reflect.construct() must be a function"
+                "First argument of Reflect.construct() must be a constructor"
             );
         });
     });