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
This commit adds the fast and CommonMark compliant Goldmark as the new default markdown handler in Hugo.
If you want to continue using BlackFriday as the default for md/markdown extensions, you can use this configuration:
```toml
[markup]
defaultMarkdownHandler="blackfriday"
```
Fixes#5963Fixes#1778Fixes#6355
