Introduce a new transformation on structured ops that splits the iteration

space into two parts along the specified dimension. The index at which the

splitting happens may be static or dynamic. This transformation can be seen as

a rudimentary form of index-set splitting that only supports the splitting

along hyperplanes parallel to the iteration space hyperplanes, and is therefore

decomposable into per-dimension application.

It is a key low-level transformation that enables independent scheduling for

different parts of the iteration space of the same op, which hasn't been

possible previously. It may be used to implement, e.g., multi-sized tiling. In

future, peeling can be implemented as a combination of split-off amount

computation and splitting.

The transformation is conceptually close to tiling in its separation of the

iteration and data spaces, but cannot be currently implemented on top of

TilingInterface as the latter does not properly support `linalg.index`

offsetting.

Note that the transformation intentionally bypasses folding of

`tensor.extract_slice` operations when creating them as this folding was found

to prevent repeated splitting of the same operation because due to internal

assumptions about extract/insert_slice combination in dialect utilities.