[mlir][Linalg] Retire C++ MatmulOp in favor of a linalg-ods-gen'd op.

This revision replaces MatmulOp, now that DRR rules have been dropped.
This revision also fixes minor parsing bugs and a plugs a few holes to get e2e paths working (e.g. library call emission).

During the replacement the i32 version had to be dropped because only the EDSC operators +, *, etc support type inference.

Deciding on a type-polymorphic behavior, and implementing it, is left for future work.

Differential Revision: https://reviews.llvm.org/D79762