Replaces a linalg.add with one operand the single user of a contraction,
which has a zero-filled, "identity-mapped" destination and is dominated
by the `other` operand, by the contraction with `other` as its dest.
Benefits include elision of an elementwise op, namely the linalg.add,
and removing a tensor.empty as a destination which is likely to require
an allocation upon bufferization.
