Check for form elements by property instead of specific element names

[mojavelinux]

Check for an input name based on whether it has the property "readOnly" and the value is false instead of checking for element names. It's both faster and more accurate.

[mojavelinux]

Actually, it seems like the most accurate way to detect a form element is to check if it has the "disabled" property (disregarding the value as disabled elements can't receive events).

That leaves us with:

('disabled' in element) || element.contentEditable === 'true'

Originally I was going to check for a readOnly element, but Firefox lets you move the cursor around in a readOnly element, so that seems useful to preserve.

[mojavelinux]

To clarify, select elements don't have the readOnly property (if you can't believe it) which is why we can't use it. Clearly we can't agree on a single definition of read only in HTML :)