Currently, when using a `Form.Check.Label` component to customize
`Form.Check` rendering, there will be no space between the checkbox and
the label. This is because `Form.Check` is currently relying on the
presence of a `label` prop to apply the `form-check` class name to the
wrapping `<div>`, because checkboxes without labels [don't need the
wrapping element to have the `form-check` class name][1].

This commit adds a utility to check whether an element has a child of a
certain type. It then uses that utility to check if a `Form.Check`
element has a `Form.Check.Label` child and takes that into account when
determining whether the checkbox has a label.

Adding a special property (currently called `typeName`, but that can
certainly change) to components for this utility is necessary because
React minifies the `displayName` property in production.

[1]: react-bootstrap#5938 (comment)

Currently, `Form.Check` doesn't allow users to use a custom
`Form.Check.Input` with a label generated by the `label` prop (and
requires that a custom `Form.Check.Input` be used if a custom
`Form.Check.Label` is also used) because the presence of _any_ children
in `Form.Check` prevents automatic inputs and labels (and feedback) from
generating. This approach allows mixing and matching by extracting any
custom input, label, and feedback components from `Form.Check`'s
`children` prop, then separately for each, using the custom component if
provided or an automatic component otherwise.

The `type` property of React elements have reference equality with
matching imported component variables (`JSXElementConstructor` objects,
to be precise)! For some reason I was not expecting that, but it makes
sense to me now, since these constructor objects are being imported from
a singular source, so there's no reason React would create multiple
instances of them. So `child.type === type` all we need to check in
`getChildOfType`; the `typeName` prop I added earlier is not at all
needed.

Just as a convenience. I can revert this commit if these scripts aren't
desired.

No idea how that got into 0754b49.

This reverts commit 5343b0a.