A single-valued set/map is not necessarily single-valued anymore after
applying after gisting a context. In particular, the set/map might not
be single-valued outside the context.
Convert the result of MemoryAccess::getAddressFunction() directly to
pw_aff. Since it is the result of lexmin(), it is single-valued by
definition. Gist the context only after te conversion.
We should consider using `isl_basic_map_partial_lexmin_pw_multi_aff` in
`getAddressFunction()` directly to avoid the intermediate step.
Fixes#190459
6b7d1a494b