Add factory functions for InputType subclasses. It is a little risky to have RefCounted subclasses with a public constructor.
Pull request: https://github.com/WebKit/WebKit/pull/12892
Committed 263114@main (29010c0f998e): <https://commits.webkit.org/263114@main> Reviewed commits have been landed. Closing PR #12892 and removing active labels.
<rdar://problem/108240397>