swift

393b4ceb - [NameLookup] Move macro-related name lookup operations into the namelookup

[NameLookup] Move macro-related name lookup operations into the namelookup namespace. This moves the `isInMacroArgument` predicate and `lookupMacros` into `namelookup`. ASTScope still encapsulates the scope tree and contains the operation to lookup the enclosing macro scope, which then invokes a callback to determine whether a potential macro scope is indeed a macro, because answering this question requires name lookup.