[Macros] Fix an issue where the constraint system skipped local declarations
inside closures while type checking a macro expansion.
PreCheckExpr, ConstraintGenerator, and other walkers do not walk into macro
expansions. However, the implementation of this macro walking behavior in
ASTWalker would skip any declaration that appears inside any macro expansion
buffer. This is incorrect for cases where the parent is in the same macro
expansion buffer, because the local declaration is not inside a new macro
expansion. This caused bogus errors when type checking expanded macro expressions
containing closures with local declarations, because pre-check and constraint
generation mistakenly skipped local pattern bindings.
(cherry picked from commit 265c8a47d97256457205f6fd90e5b801b4c924f2)