markup/goldmark: Add Position to CodeblockContext

But note that this is not particulary fast and the recommendad usage is error logging only.

Updates #9574

markup/converter/converter.go

@@ -128,9 +128,13 @@ type DocumentContext struct {
 
 // RenderContext holds contextual information about the content to render.
 type RenderContext struct {
-	Src       []byte
+	// Src is the content to render.
+	Src []byte
+
+	// Whether to render TableOfContents.
 	RenderTOC bool
 
+	// GerRenderer provides hook renderers on demand.
 	GetRenderer hooks.GetRendererFunc
 }