AsciiDoc references don't work when a custom reference is assigned
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### Summary
When defining a cross reference (`[[ref]]` or `[#ref]`) to a section, image, or similar, that reference can't be resolved by GitLab's preview.
### Steps to reproduce
Create a `file.adoc` in your repository with e.g. the following content
```adoc
= My Document
See [[secAnother]].
// Insert some text to achieve vertical spacing
== A section
// Insert some text to achieve vertical spacing
[[secAnother]]
== Another section
// Insert some text to achieve vertical spacing
```
With this file previewed in GitLab, I can create a link to `A section` by clicking the link symbol left of it. The created link will look something like `...branch/file.adoc#user-content-a-section`. I can't do this for `Another section`. The link will end in `...branch/file.adoc#secAnother`, which is not resolved to the correct vertical position by GitLab.
### Example Project
https://gitlab.com/cbachhuber/asciidoc-playground
### What is the current *bug* behavior?
When clicking the link left of Section `5.6.3 DOCX`, this link (https://gitlab.com/cbachhuber/asciidoc-playground#docx) is opened and I'm forwarded to a seemingly random vertical position. This is because I assigned cross reference `[#docx]` to this section. Section links without a user-defined cross reference work fine, e.g. the link to the first chapter (https://gitlab.com/cbachhuber/asciidoc-playground#user-content-first-chapter).
User-defined cross references also destroy links from references within the document, such as entry 3 of the table of contents, which resolves to https://gitlab.com/cbachhuber/asciidoc-playground#alternative_heading. Other ToC entries work as expected.
With canonical asciidoctor tools, all cross references in my repository are resolved as expected, so I'm using correct syntax.
### What is the expected *correct* behavior?
Correct vertical scrolling to the referenced item (section, image, table etc.).
### Possible fixes
Can probably be solved by keeping the `#user-content-item` URL ending instead of replacing it with `#referenceName`.
issue