[mlir][tensor][linalg] Add a pattern that generalizes tensor.unpack op.

The pattern generalizes a tensor::UnPackOp into a sequence of tensor +
Linalg ops, when the outer dims are all 1s. It uses the trick of
rank-reduced tensor.extract_slice to get the tile; transpose the tile;
extract sub tile for incomplete cases if needed; use tensor.insert_slice
to insert it to the destination tensor.

Reviewed By: tyb0807, chelini

Differential Revision: https://reviews.llvm.org/D140254