Add Parent Visitee to key Visitees (Option, EnumField, etc)?

[bufdev]

For Option specifically, if I'm writing a formatter, I need to know what type of option it is (message option, rpc method option, etc). I could have a completely new visitor for this but this seems overkill.

[bufdev]

This can be mitigated by having a parent Visitee field in the struct that implements Visitor:

func (v *logVisitor) VisitEnum(element *proto.Enum) {
	v.logVisitee(element)
	originalParent := v.parent
	v.parent = element
	for _, child := range element.Elements {
		child.Accept(v)
	}
	v.parent = originalParent
}