[libc++][numeric] P0543R3: Saturation arithmetic (#77967)

Implements: https://wg21.link/P0543R3
- https://eel.is/c++draft/numeric.sat

Additional references:
- Division: https://eel.is/c++draft/expr.mul#4
- Arithmetic conversions: https://eel.is/c++draft/expr.arith.conv#1
- Clang builtins:
https://clang.llvm.org/docs/LanguageExtensions.html#builtin-functions

Depends on: https://github.com/llvm/llvm-project/pull/78086

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Co-authored-by: Zingam <zingam@outlook.com>
Co-authored-by: Mark de Wever <zar-rpg@xs4all.nl>
GitOrigin-RevId: 03c19e91e8d8cb706b58e02d69f80caeaf7eb0f4
24 files changed