Now that Goldmark has a Node.Pos() (in >= v1.8.0) we can do better, so that should make it easier/cheaper to calculate, so I suggest that we

• Add .Position to all render hooks (which makes all hooks at least implement the interface below).
• Simplify the implementation.

type BaseContext interface {
	Position() Position
	Page() any
	PageInner() any
	Ordinal() int
}