Remove interactive content and form related API from HTMLElement.

In particular this inlines the accessKeyAction, removes isInteractiveContent()
which was for special casing certain elements in event dispatch, and removes
eventParameterName() which was only needed for inline event handlers.

I also moved Node::commonAncestor into NodeRenderingTraversal, the only
callers of it passed NodeRenderingTraversal::parent as the second argument,
it didn't make sense to have this generic thing.

R=abarth@chromium.org, ojan@chromium.org

Review URL: https://codereview.chromium.org/693243002