Replace obsolete ToInteger() for checking an Integer

As by the spec the method ToInteger() should be used to check if the given Number is an integer.

https://w3c.github.io/webdriver/#dfn-integer

An integer is a Number that is unchanged under the ToInteger operation.

But the MDN web docs claim this method to be obsolete, and it never reached the ES6 final specification:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toInteger

As such an alternative should be used. Also given that we shouldn't directly compare an integer and a float, Number.EPSILON might have to be taken into account. But maybe this is neglected given that no-one might specify a timeout with such a precision.

What's in the ECMAScript specification for a long time is toFixed(), which is supported by every browser.

I propose the following:

An integer is a Number that is unchanged under the toFixed operation.

The issue names no files or tests. Start with the WebDriver integer definition and compare its ToInteger reference with the cited ECMAScript and MDN material, then trace where the definition is used in the specification. Done means agreeing on a standards-compatible replacement and updating all affected wording consistently.