This reverts commit 620adacf87.
Fix: unsupport C++03 for the new test, define helpers before __swap_allocator
(1) Add _VSTD:: qualification to __swap_allocator.
(2) Add _VSTD:: qualification consistently to __to_address.
(3) Add some more missing _VSTD:: to <vector>, with a regression test.
This part is cleanup after d9a4f936d0.
Note that a vector whose allocator actually runs afoul of any of these ADL calls will
likely also run afoul of simple things like `v1 == v2` (which is also an ADL call).
But, still, libc++ should be consistent in qualifying function calls wherever possible.
Relevant blog post: https://quuxplusone.github.io/blog/2019/09/26/uglification-doesnt-stop-adl/
Differential Revision: https://reviews.llvm.org/D91708
6e965df605