When rendering an AsciiDoc document, we should set the default value of the "stem" attribute to "latexmath"

Problem to solve

By default, Asciidoctor assumes that all equations are AsciiMath if not specified explicitly. Since GitLab does not support AsciiMath, the following won't be rendered automatically:

[stem] 
++++ 
sqrt(4) = 2
++++

A matrix can be written as stem:[[[a,b\],[c,d\]\]((n),(k))].

The users need to explicitly define :stem: latexmath. For reference, in GitLab, STEM support is provided by KaTex (client-side).

Intended users

People that write documentation.

User experience goal

Seamlessly enable STEM support. The users won't have to explicitly define :stem: latexmath when the document is rendered in GitLab.

Proposal

We should set the default value of the stem attribute to latexmath in order to render stem inline and block macros with KaTeX.

The value should be defined using the @ modifier to set a lower-precedence. In other words, if the user explicitly define the stem attribute in its document, we should not override the value.

Documentation

We should update the documentation at https://docs.gitlab.com/ee/user/asciidoc.html to explain how STEM support is implemented in GitLab.

What does success look like, and how can we measure that?

GitLab should render the following equations using KaTex:

[stem] 
++++ 
sqrt(4) = 2
++++

A matrix can be written as stem:[[[a,b\],[c,d\]\]((n),(k))].

Links / references

https://asciidoctor.org/docs/user-manual/#activating-stem-support