Executes sync script on a page.

Pass arguments to function as additional parameters.

Will return execution result to a test.

In this case you should use async function and await to receive results.

Example with jQuery DatePicker:

```js

// change date of jQuery DatePicker

I.executeScript(function() {

});

```

Can return values. Don't forget to use `await` to get them.

```js

let date = await I.executeScript(function(el) {

}, '#date'); // passing jquery selector

```

@param {string|function} fn function to be executed in browser context.

@param {...any} args to be passed to function.

@return {Promise<any>}