Implement cross-driver $element->executeJs()

I've found myself in a corner more than once, trying to use the built in search traversal with JS methods.

One example of that would be interacting with <select> augmenting JS scripts (selectable, select2 etc.). In order to work around issues with those, I need to be able to invoke pieces of JS on some elements.

For example:

// [...] find the field to change
$field->selectOption($option, false);
$this->getSession()->evaluateScript('$("select").trigger("change");');

Currently there's no easy method to get reference to the NodeElement node in JS. Internally, Selenium2 driver uses executeJsOnXpath() method which takes a script template and "injects" the element we want to target. I'd love to be able to do this:

// [...] find the field to change
$field->selectOption($option, false);
$field->executeJs('$({{ELEMENT}}).trigger("change");');

Start by tracing NodeElement and the Selenium2 driver's executeJsOnXpath() method, then review how the session's evaluateScript() is used. Implement the cross-driver element execution API so the target element can be referenced in the script, and verify the select-option change-event example works across supported drivers.