[flang][hlfir] relax the strictness of intrinsic verifiers

The verifiers for hlfir.matmul and hlfir.transpose try to ensure that
the shape of the result value makes sense given the shapes of the input
argument(s).

It there are some cases in the gfortran tests where lowering knows a bit
more about shape information than (HL)FIR. I think the cases here will be
solved when hlfir.shape_meet is implemented.

But in the meantime, and to improve robustness, I've relaxed the
verifier to allow the return type to have more precise shape information
than can be deduced from the argument type(s).

Differential Revision: https://reviews.llvm.org/D152254