Add a conditional state object

[dphfox]

Partial alternative to #377.

A more specific state object may be introduced for simple conditions:

local animShow = scope:If(show, 0.0, 1.0)

This would allow lazy evaluation of arguments.

[znotfireman]

My I recommend the name Switch or Toggle to match other libraries (e.g. Vide has the switch utility)

[dphfox]

We generally look to align with Luau, not outside libraries.

As a case study of why we don't do this, we originally aligned Value's naming with React - "State" - and it brought no material benefit. Instead, it just confused everyone, even though ostensibly React was serving UI developers all the same.

So we name things based on Luau as a general universal baseline, rather than imposing knowledge requirements on our users to understand what names mean.

In this case, both "Switch" and "Toggle" sound more like actions or stateful objects. Instead, this object represents a control flow expression. So the name instead tries to mirror Luau's if expression.