[flang] Be more precise about CHARACTER known length discrepancies

Many intrinsic functions in Fortran require that two or more of their
arguments have types that agree in the values of all of their type
parameters, while others only require the same type category and kind
type parameters but not lengths, including the important case of
CHARACTER.  The intrinsic procedure tables need to be adjusted in
some cases so that discrepancies in character lengths that are known
at compilation time can be diagnosed as errors where they should be,
as in for example MOVE_ALLOC().

Differential Revision: https://reviews.llvm.org/D137032