Fix handling of reference links with inline code

[Trott]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

This fixes the AST so that certain kinds of reference links are not
broken when converted back to markdown.

Fixes: remarkjs/remark#850

[Trott]

I don't know if this is the right fix for remarkjs/remark#850, but it fixes that issue without breaking any existing tests, so I'm hopeful....

[wooorm]

Nice catch! It looks like definitions do get a proper identifier and label, but for link (and image?) references it’s broken.

There is probably a problem with character references and character escapes though. Take this example:

[`f`][]
[;][]
[\;][]
[;][]
[`f`;][]
[`f`\;][]
[`f`;][]

[`f`]: alpha
[;]: bravo
[\;]: charlie
[;]: delta
[`f`;]: echo
[`f`\;]: foxtrot
[`f`;]: golf

Note that one might expect that character references and -escapes and the actual value would match, but CommonMark does not:

<p><a href="alpha"><code>f</code></a>
<a href="bravo">;</a>
<a href="charlie">;</a>
<a href="delta">;</a>
<a href="echo"><code>f</code>;</a>
<a href="foxtrot"><code>f</code>;</a>
<a href="golf"><code>f</code>;</a></p>

Looking at the AST that remark produces, the definitions work properly: the character references and -escapes are handled properly in label/identifier. The same is true for link (and image?) references, but there the code (and probably other things such as emphasis), as you found out, don’t work.

[wooorm]

I was able to verify that micromark does handle this correctly: micromark/micromark@5be7549

[wooorm]

Thanks @Trott, this helped a lot. Released!