markup/goldmark: Add removeSurroundingParagraph for Markdown images

* Removes any surrounding paragraph nodes
* And transfers any attributes from the surrounding paragraph down to the image node
* Adds IsBlock and Ordinal (zero based) field to the image context passed to the image render hooks

IsBlock is set to true if `wrapStandAloneImageWithinParagraph = false` and  the image's parent node has only one child.

Closes #8362
Fixes #10492
Fixes #10494
Fixes #10501

markup/internal/attributes/attributes.go

@@ -126,6 +126,9 @@ func (a Attribute) ValueString() string {
 	return cast.ToString(a.Value)
 }
 
+// Empty holds no attributes.
+var Empty = &AttributesHolder{}
+
 type AttributesHolder struct {
 	// What we get from Goldmark.
 	attributes []Attribute