[mlir][Linalg] Use reify for padded op shape derivation.

Previously, we would insert a DimOp and rely on later canonicalizations.
Unfortunately, reifyShape kind of rewrites are not canonicalizations anymore.
This introduces undesirable pass dependencies.

Instead, immediately reify the result shape and avoid the DimOp altogether.
This is akin to a local folding, which avoids introducing more reliance on `-resolve-shaped-type-result-dims` (similar to compositions of `affine.apply` by construction to avoid chains of size > 1).

It does not completely get rid of the reliance on the pass as the process is merely local: calling the pass may still be necessary for global effects. Indeed, one of the tests still requires the pass.

Differential Revision: https://reviews.llvm.org/D109571