Add .Position to the context of heading and image render hooks

[bowman2001]

The codeblock render hook context includes the .Position of the current codeblock in a local Markdown file.

It would be nice to have this information also for heading and image render hooks. This would allow to include links to the source in local server mode.

[bep]

I agree that this would be nice to have, but it's non-trivial to implement. The implementation we have for code blocks is expensive/slow. The main challenge is the shortcodes with {{< delimiters; the position you get when parsing the Markdown (Goldmark, assuming that info is there) does not take the shortcodes into account. And if you think about the new {#11320 ... there's lots to think about, as Position may well point to a different Markdown file.

[bowman2001]

I’ve hoped this would be relatively easy. So it can wait, it’s certainly not a priority.