* Record the leading whitespace (tabs, spaces) before the shortcode when parsing the page.
* Apply that indentation to the rendered result of shortcodes without inner content (where the user will apply indentation).
Fixes #9946
You can turn off this behaviour:
```toml
[markup]
[markup.goldmark]
[markup.goldmark.parser]
autoHeadingIDAsciiOnly = true
```
Note that the `anchorize` now adapts its behaviour depending on the default Markdown handler.
Fixes #6616
