[mlir][Vector] Fold ShuffleOp if result is identical to one of source vectors.

For example, we could do the following eliminations:
  fold vector.shuffle V1, V2, [0, 1, 2, 3] : <4xi32>, <2xi32> -> V1
  fold vector.shuffle V1, V2, [4, 5] : <4xi32>, <2xi32> -> V2

Differential Revision: https://reviews.llvm.org/D122706