WG21-P3247R2 Deprecate The Notion Of Trivial Types

This is a Core paper with Library impact. In addition to deprecating is_trivial and is_trivial_v, there are other Library wording updates that might affect product or test code.

No feature-test macro is mentioned.

Note: We're focused on implementing the remaining library-only features in C++23. Until that's done, we will NOT be accepting PRs for C++26 features.