Fixes: https://bugs.webkit.org/show_bug.cgi?id=25617

Fix memory/performance regression because of too much form control related abstraction just for WMLs sake.

Remove FormControlElement and FormControlElementWithState base classes, as the overhead is too high for the
gain. HTML has no benefit of that kind of abstraction, so we're going to move the functionality to Element directly.

The functions now living in FormControlElement(WithState) lived in Node/Element/HTMLFormControlElement before.
This patches moves all of them in a central place in Element.h, as virtual functions with an inline default implementation.
To avoid confusion like isEnabled() living on Node, before the creation of the FormControlElement abstraction layer, all
methods are renamed to clarify where they belong to. (Detailed list in ChangeLog)


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@43367 268f45cc-cd09-0410-ab3c-d52691b4dbfc