Align Checkbox and RadioButton components

[connor-baer]

• The label for a Checkbox is defined by the Checkbox element's children while the label for a RadioButton is defined by the label prop.

This should be aligned in a future major. All input components should accept a label prop, not children. But out of scope of this one.

Originally posted by @robinmetral in #1815 (comment)

I suppose we could do the same for the RadioButtonGroup right?

Unlike the Checkbox, the RadioButton doesn't wrap its input and label in a wrapper div. I would add a wrapper to the RadioButton component in the next major to align the components.

Originally posted by @connor-baer in #1851 (comment)