feat: allow Select to more easily support filtering via extension

[atmgrifter00]

🙋 Feature Request

We have a need to provide filtering capability for the Select, which was a mostly painless process, save for one unfortunate implementation hack. Ultimately, we had to provide an override to the set value implementation so we could reference our overridden options reference which returns a filtered set of options (just like the Combobox). However, in the Select base implementation it ultimately sets its private _value field. The only solution I had was to sidestep our linter and do something like this['_value'] = newValue;.

I'm not sure if the ultimate answer is to make _value protected or some other more official extensibility support, but I think the ideal results in clients not having to write the kind of code I mention above.

🤔 Expected Behavior

I should be able to extend Select to provide filtering support without having to write non-type safe code.

😯 Current Behavior

Couldn't come up with a way to provide the behavior I needed without writing non-type safe code (ala this['_value'] = newValue;).

💁 Possible Solution

Make _value protected.

🔦 Context

💻 Examples

[chrisdholt]

I'm not against enabling extensibility through protected methods. _value is interesting, but in some sense, if you're going to take extend there is an author responsibility in my mind on doing that. I also think there is value is that over increasing complexity within the base component.

Thoughts from @kingoftac, @radium-v, @bheston, @scomea?

[janechu]

Unfortunately @microsoft/fast-foundation is being deprecated, refer to #6955.