[mlir] [VectorOps] Correctly account for rank-0 affine-map result in vector.contract

[mlir] [VectorOps] Correctly account for rank-0 affine-map result in vector.contract

Summary:
Now that, thanks to ntv, we have the ability to parse and represent an affine
map with rank-0 results, viz. (i,j) -> (), we can pay off some engineering debt
in special casing the verification of such affine maps in dot-product flavored
vector.contract operations.

Reviewers: nicolasvasilache, andydavis1, rriddle

Reviewed By: nicolasvasilache

Subscribers: mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, liufengdb, Joonsoo, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76028