[flang][hlfir] Add hlfir.dot_product intrinsic

Adds a new HLFIR operation for the DOT_PRODUCT intrinsic according to
the design set out in flang/docs/HighLevel.md. This patch includes all
the necessary changes to create a new HLFIR operation and lower it into
the fir runtime call.

Differential Revision: https://reviews.llvm.org/D152252