New versions of Sphinx use `latexmk` to build the PDF files. This
command uses a file called `latexmkrc` (or `latexmkjarc` for Japanese)
which contains all the proper commands that needs to be ran depending
on different Sphinx configurations.

`latexmk` will take care by itself on the amount of phases that need
to be ran without us worrying about it.

Currently, this is not considering LATEXMKOPTS and XINDYOPTS
environment variables configured by Sphinx.

This feature is implemented under a Feature flag so we can test it
easily without breaking other working projects.

References:

- #1556
- #4454
- #5405
- toppers/tecs-docs#7
- https://github.com/sphinx-doc/sphinx/blob/master/sphinx/texinputs/Makefile_t
- https://www.sphinx-doc.org/en/master/usage/builders/index.html#sphinx.builders.latex.LaTeXBuilder

Automatically select `xelatex` for Chinese and `platex` for Japanese.
These defaults can be overridden by the user.

Force `latex_use_xindy=False` for now until we support it in our
Docker image.