Fix FormSelect to consume isRequired prop through context

[jenny-s51]

This issue is an extension to #1397 and PR #2365

Currently, it looks like FormGroup uses context to consume the isRequired prop from the parent Form component. The isRequired prop also ends up showing up in any child component of FormGroup, like TextInput for example. This is the expected behavior of the isRequired prop, per @jgiardino.

At the moment,FormSelect doesn't do the same thing with context.

This would be a good enhancement to make if we're trying to stay consistent among all form components.