[libcxx] adds concept `std::copy_constructible`

Implements parts of:
    - P0898R3 Standard Library Concepts
    - P1754 Rename concepts to standard_case for C++20, while we still can

Depends on D96230

Differential Revision: https://reviews.llvm.org/D96232

GitOrigin-RevId: 2193e8be3efa5eea452c6c5bbc2f6393c8f10e62
2 files changed