Summary: (@kevinbarabash)
This diff extracts MathML builder tests out into a separate file and
updates them to use jest snapshot testing. It updates the output of
prime ' from using identifier nodes <mi> to operator nodes <mo>. It
also updates large operators with limits to use munderover instead
of msupsub. I added an option to remove unnecessary mrows to buildGroup.
Right now it's only used for by groupTypes.supsub. I'll see if it can be used
elsewhere (everywhere?) in a follow up PR.
Test Plan:
- make test w/o errors
- verify mathml snapshots contain the desired markup
