[flang] Make `TypeParamInquiry` monomorphic

Change the expression representation TypeParamInquiry from being
a class that's templatized on the integer KIND of its result into
a monomorphic representation that results in a SubscriptInteger
that can then be converted.

This is a minor simplification, but it's worth doing because
it is believed to also be a work-around for bugs in the MSVC
compiler with overload resolution that affect the expression
traversal framework.

Differential Revision: https://reviews.llvm.org/D86551