[StructuredOps][Linalg] Add a primitive pattern to rewrite the linalg.generic...

[StructuredOps][Linalg] Add a primitive pattern to rewrite the linalg.generic form of matmul to vector form.

This CL uses the newly expanded matcher support to easily detect when a linalg.generic has a multiply-accumulate body. A linalg.generic with such a body is rewritten as a vector contraction.
This CL additionally limits the rewrite to the case of matrix multiplication on contiguous and statically shaped memrefs for now.

Before expanding further, we should harden the infrastructure for expressing custom ops with the structured ops abstraction.

PiperOrigin-RevId: 284566659