[libc++] Investigate the precondition fix in P3179R9 for existing algorithms

[P3179R9](https://wg21.link/p3179r9) (tracked in #148138 and numerous sub-issues) fixed preconditions for the following algorithms, for both `std` and `ranges` versions:
- `copy`
- `copy_if`
- `move`
- `transform`
- `replace_copy`
- `replace_copy_if`
- `remove_copy`
- `remove_copy_if`
- `unique_copy`
- `partition_copy`
- `set_union`
- `set_intersection`
- `set_difference`
- `set_symmetric_difference`

I think the precondition fix should be treated as an LWG DR as it probably superseded [LWG4262](https://cplusplus.github.io/LWG/issue4262) (as noted in https://github.com/microsoft/STL/pull/5683#discussion_r2488923707). Perhaps we should investigate whether our precondition checks (if any) are still correct.