Highlight.js upgrade breaks mrdocs links

I've upgraded the UI bundle from https://github.com/boostorg/website-v2-docs/releases/download/ui-master/ui-bundle.zip to https://github.com/boostorg/website-v2-docs/releases/download/ui-develop/ui-bundle.zip. All MrDocs generated links in the reference have disappeared. Looking at commit history, this is very much likely due to #400.

This is the asciidoc that mrdocs is rendering:

```adoc
[#boost-mysql-any_connection-meta_mode]
= xref:boost.adoc[boost]::xref:boost/mysql.adoc[mysql]::xref:boost/mysql/any_connection.adoc[any_connection]::meta_mode
:relfileprefix: ../../../
:mrdocs:

Returns the current metadata mode that this connection is using.

== Synopsis

Declared in `<https://github.com/boostorg/mysql/blob/master/include/boost/mysql/any_connection.hpp#L339[boost/mysql/any_connection.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:boost/mysql/metadata_mode.adoc[metadata_mode]
meta_mode() const noexcept;
----

== Description

=== Exception safety

No‐throw guarantee.

== Return Value

The metadata mode that will be used for queries and statement executions.

[.small]#Created with https://www.mrdocs.com[MrDocs]#
```

Master UI renders:


Develop UI renders: