There's a lot of details to flesh out here, but the basic approach seems
promising (see comments in createE2ELoweringPipeline).
This approach will be put to the test when we try to do our first
fusions since that tickles some of the nasty phase ordering issues
involved here.
But we're not there yet.
This makes sure we stay resonably canonically using the shape machinery.
(In fact, DimOp should probably be in the shape dialect since it hides a
`shape.shape_of` call)
Sean Silva