Fix AffineApply corner case

This CL adds a test reported by andydavis@ and fixes the corner case that
appears when operands do not come from an AffineApply and no Dim composition
is needed.

In such cases, we would need to create an empty map which is disallowed.
The composition in such cases becomes trivial: there is no composition.

This CL also updates the name AffineNormalizer to AffineApplyNormalizer.

PiperOrigin-RevId: 229819234