Given an array of fields to include in a response, some of which may be
`nested.fields`, determine whether the provided field should be included
in the response body.

If a parent field is passed in, the presence of any nested field within
that parent will cause the method to return `true`. For example “title”
will return true if any of `title`, `title.raw` or `title.rendered` is
provided.

function rest_is_field_included( $field, $fields ) {
	if ( in_array( $field, $fields, true ) ) {
		return true;
	}

	foreach ( $fields as $accepted_field ) {
		// Check to see if $field is the parent of any item in $fields.
		// A field "parent" should be accepted if "parent.child" is accepted.
		if ( strpos( $accepted_field, "$field." ) === 0 ) {
			return true;
		}
		// Conversely, if "parent" is accepted, all "parent.child" fields
		// should also be accepted.
		if ( strpos( $field, "$accepted_field." ) === 0 ) {
			return true;
		}
	}

	return false;
}