feat: pass answers to validator function

[DesignByOnyx]

This closes #273

I don't consider this done yet, but I wanted to go ahead and take a stab at this and get some feedback. Tasks still remaining:

• since I'm here, should all elements support validation (Support validate on multiselect #344 and others)?
• update the docs

This is not my favortie implementation, but it's the best I could come up with short of a refactor. The crux of the problems is we need to pass the answers to all elements as they are constructed. In an ideal world the question and answers would be passed as two separate arguments to the element constructors. I'm glad to make that change, though it will touch a lot more files and lines of code.

[DesignByOnyx]

I needed this again today and prefer not to use my fork. I have time, availability, and eagerness to implement this. I will write tests and ensure there are no breaking changes. Any feedback from the team would be great... even if it's in the form of "we don't have time to review this, and it probably wont get merged" would help. Thanks!