Global peer macro expansions are not injected into the AST. Instead, they
are visited as "auxiliary declarations" when needed, such as in the decl
checker and during SILGen. This is the same mechanism used for local property
wrappers and local lazy variables.
Extend the macro-expansion refactoring to work with member and
member-attribute attached macros. These expansions can return several
different changes, e.g., adding new members, sprinkling member
attributes around, and so on.
- Use the name lookup table instead of adding members from a macro expansion to the parent decl context.
- Require declaration macros to specify introduced names and used the declared names to guide macro expansions lazily.
