[libcxx] adds concept std::movable

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

Depends on D97162

Reviewed By: EricWF, #libc, Quuxplusone

Differential Revision: https://reviews.llvm.org/D97359

GitOrigin-RevId: dc9f385722245858a2d5160d5764158195e3751e
9 files changed