Add output type information to BindingData

[marner2]

This Pull Request adds another type parameter to BindingData which allows it to carry the actual view model property type statically through the builder.

From a conversation with @TysonMN:

When used in the context of "dot" notation in the XAML project, you will be able to get compile-time help for things like ViewModelProp.SubModel.Prop. If those were constrained to obj, you wouldn't get compile-time checking of those types.
Also XAML will warn you about type issues (number vs string, etc)

Note that the current usage of Binding<'model,'msg> constrains the new type parameter to be obj for every construction of it (this is the entire public interface in Binding.fs). This is intentional, as all of those bindings are by necessity constrained to obj in order to work in the various SubModel and SubModelSeq bindings. The advantage mentioned above will not be realized until after a static helper is created that can turn a binding into a statically-typed getter or setter.

[TysonMN]

Both the GutHub App and FastHub seem to be showing me weird white space changes. I want to review this on my laptop.

[TysonMN]

Not part of this PR:
On line 669 of BindingVmHelpers, lets rename x to result

[marner2]

@TysonMN I put #498 before this one now, since I was rebasing a lot. That one now needs to be merged in first

[TysonMN]

For each comment that had a pin put in it, can you add a comment on the new PR that is adding that code, link back to the pinned comment here, quote what I asked, and (if you responded here) quote your response?

[LyndonGingerich]

For each comment that had a pin put in it, can you add a comment on the new PR that is adding that code, link back to the pinned comment here, quote what I asked, and (if you responded here) quote your response?

Done for every comment explicitly referenced as pinned for a future PR.