* rollback some previous changes for ce env in Parserhookhandler
* some minor fixes for feedback in previous commit
* set tex mode for mhchem preprocessor, since MediaWiki Hooks add
explicit ce tags: i.e. frormula coming to TexVC look like
"{\displaystyle \ce{ C6H5-CHO }}"
Bug: T348975
Change-Id: Id06852b030f9ea77f016289d4f9e2258d5a9f0d4
* defaults mathchoice to displaystyle
* adds several tests and introduces new Fun4 element for mathchoice in
grammar
Bug: T340024
Change-Id: I37c8fd35303e3b8a00faad18a3a131a716c7bb47