P3019R14 `indirect` And `polymorphic`: Vocabulary Types For Composite Class Design

[StephanTLavavej]

WG21-P3019R14 indirect And polymorphic: Vocabulary Types For Composite Class Design
LWG-4251 Move assignment for indirect unnecessarily requires copy construction
LWG-4325 std::indirect's operator== still does not support incomplete types
LWG-4532 Imprecise std::polymorphic wording seems to imply slicing

Feature-test macro:

#define __cpp_lib_indirect 202502L
#define __cpp_lib_polymorphic 202502L

Note: We are not yet accepting PRs for C++26 features.