The operations `to_extent_tensor` and `from_extent_tensor` become no-ops when
lowered to the standard dialect.
This is possible with a lowering from `shape.shape` to `tensor<?xindex>`.
Differential Revision: https://reviews.llvm.org/D81162
Add a new pass to lower operations from the `shape` to the `std` dialect.
The conversion applies only to the `size_to_index` and `index_to_size`
operations and affected types.
Other patterns will be added as needed.
Differential Revision: https://reviews.llvm.org/D81091