parseFormula
parseFormula:
FnParseFormula|null=null
Formula parser function, if formula parser has finished (asynchronously) importing, else null.
This can be called from synchronous code which itself is guaranteed to be executed only after the formula parser
has finished importing. The caller is then responsible for enforcing that guarantee, and/or documenting that its
callers must enforce it, and/or guarding against this being null with appropriate error handling.