The Reference to bot.dom.isShown is Incompatible with its Signature

[jginsburgn]

In chapter C. Element displayedness:

To compute the state on element, invoke the Function.[[Call]](null, element), with bot.dom.isShown as the this value

I detected two problems with the reference to the bot.dom.isShown function:

1. The linked symbol is: bot.dom.isShown_, with an underbar. The spec should be cohesive when naming and linking symbols.
2. The signature of the actual function has 3 arguments, while the spec only refers to 1, leaving the other two undefined.

I guess that the function that should have been linked is https://github.com/SeleniumHQ/selenium/blob/e09e28f016c9f53196cf68d6f71991c5af4a35d4/javascript/atoms/dom.js#L550. Linking that one solves issue 1 and reduces the discrepancy defined in issue 2.