[mlir][tensor][NFC] Rename linalg.init_tensor to tensor.empty

tensor.empty/linalg.init_tensor produces an uninititalized tensor that can be used as a destination operand for destination-style ops (ops that implement `DestinationStyleOpInterface`).

This change makes it possible to implement `TilingInterface` for non-destination-style ops without depending on the Linalg dialect.

RFC: https://discourse.llvm.org/t/rfc-add-tensor-from-shape-operation/65101

Differential Revision: https://reviews.llvm.org/D135129