[libc++][ranges] Implement ranges::uninitialized_default_construct{,_n}.
Defined in [`specialized.algorithms`](wg21.link/specialized.algorithms).
Also:
- refactor the existing non-range implementation so that most of it
can be shared between the range-based and non-range-based algorithms;
- remove an existing test for the non-range version of
`uninitialized_default_construct{,_n}` that likely triggered undefined
behavior (it read the values of built-ins after default-initializing
them, essentially reading uninitialized memory).
Reviewed By: #libc, Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D115315
NOKEYCHECK=True
GitOrigin-RevId: 3f630cff65fc6aa69f951916442a8fb1de11be65
17 files changed