Resolve "Reference parsing conflicting with auto-linking"

What does this MR do?

Fixes the auto-linker when the URL contains an ampersand, or other HTML entity. As a consequence of that, fixes links to compare between versions of an MR.

Are there points in the code the reviewer needs to double check?

I think the comment and specs cover it.

Why was this MR needed?

Regression in 10.6 😞

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #44649 (closed).