[mlir][linalg] Introduce a separate EraseIdentityCopyOp Pattern.

Split out an EraseIdentityCopyOp from the existing RemoveIdentityLinalgOps pattern. Introduce an additional check to ensure the pattern checks the permutation maps match. This is a preparation step to specialize RemoveIdentityLinalgOps to GenericOp only.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D105622