Previously gordmark-based TOC renderes only `KindText` and `KindString`
This commit expands target node with Goldmark's renderer
I am not sure of what are expected results as TOC contents in some (rare) cases
but Blackfriday's behaviours are fundamentally respected.
For example,
- image `[image text](link)` is rendered as `<img>` tag
- GFM AutoLink `gohugo.io` is rendered as text
* Render AutoLink as <a> tag as Blackfriday does
Fixes#6736Fixes#6809
ca68abf0bc