Validate BehaviorBase<T> and what is needed (if anything) beyond Behavior<T>

[michael-hawker]

We probably want to file an issue about re-checking all this, as I know some of the original issues I believe were fixed in the underlying behaviors package, but I think we still do some extra logic here.

Probably a thing where when we can better test these and shore that up, we could try removing the intermediate class and see what happens or if anything breaks. (Assuming we have enough coverage)

Originally posted by @michael-hawker in https://github.com/CommunityToolkit/Windows/pull/20#discussion_r1167170975

Related Toolkit Discussion: https://github.com/CommunityToolkit/WindowsCommunityToolkit/issues/3856

with specifically more prior context and links here: https://github.com/CommunityToolkit/WindowsCommunityToolkit/issues/3856#issuecomment-801471909