Replace all string-based TypeDef:* kind matching with a 17-variant
TypeDefKind enum. The enum provides compile-time exhaustiveness
checking, integer discriminant dispatch (jump table), and type-safe
methods (type_size, natural_alignment, is_fixed_size, etc.).
- Add TypeDefKind enum with FromStr, Display, and helper methods
- Add get_typedef_kind_enum() and get_typedef_kind_loose_enum()
- Convert DiscriminatorKind::Byte.disc_type from String to TypeDefKind
- Convert FieldPosition.kind from String to TypeDefKind
- Convert all 8 dispatch sites from string matching to enum matching
- Remove legacy string-based type_size/natural_alignment/is_fixed_size
wrapper functions — all call sites use enum methods directly
- Update tests to use enum variants
deepseek-v4-pro
ce7ef1e31f