Hygiene, for declarations

Decided

D-0076, settled by the language’s author: part of spec §18. Older text cites it as 18.76.

Locals an expansion introduces are hidden; declarations it introduces are not. A let, parameter or binding written in expand cannot capture or be captured; types, functions, methods, fields, variants and constants are ordinary declarations the caller names, and a type’s members are reachable bare from its methods as usual. Other names in expand resolve where the macro is declared. No identifier pasting. Refines §12.4’s rule, which read literally hid a generated union States from the code it was generated for (§12.4)