Disallow non-index operands and results in affine.apply

`affine.apply` is supposed to operate on values of index types in context of
affine loops.  It is possible to programmatically constuct an `affine.apply`
that takes values of other types as operands or returns them, but it would not
be parseable.  Disallow such cases in the verifier.

PiperOrigin-RevId: 253021704