[MLIR] Extend vector.gather to accept tensor as base

In addition to memref, accept ranked tensor as the base operand of vector.gather, similar to vector.trasnfer_read.

This will allow us to vectorize noncontiguous tensor.extract into vector.gather. Full discussion can be found here: https://github.com/iree-org/iree/issues/9198

Reviewed By: hanchung, dcaballe

Differential Revision: https://reviews.llvm.org/D130097