When collecting user feedback regarding the native
rendering option on the German Wikipedia (T346795)
it became apparent that some power users aim for bigger
and bolder fonts and a more LaTeX-like layout.
MathML, however, aims to format math as an integral part
of the text with uniform fonts and spacing.
To match both user needs, this patch adds a new rendering
option that uses client-side MathJax (without a need for
restbase or mathoid).
* Adjust MathJax`s loader to be compatible with the mw loader
* Add new rendering mode
* Copy MathJax source to resource module as foreign repo
Bug: T354136
Change-Id: I1ecf9c77fefc3b0f717107d81979276023f6cb84
