Do not update the jkind in update_decl_jkind if the manifest is available; always copy the manifest's jkind in check_coherence. This allows us to give types like 'a or_null non-standard jkinds for their kinds (i.e. value_or_null for Type_variant).
Pre-define or_null when Layouts has level Alpha. Add tests for or_null.
or_null will be added to stdlib_alpha in the next PR.
Do not update the jkind in
update_decl_jkindif the manifest is available; always copy the manifest's jkind incheck_coherence. This allows us to give types like'a or_nullnon-standard jkinds for their kinds (i.e.value_or_nullforType_variant).Pre-define
or_nullwhenLayoutshas levelAlpha. Add tests foror_null.or_nullwill be added tostdlib_alphain the next PR.