[libc++] Fix several double-moves in the code base (#104616)

This patch hardens the "test iterators" we use to test algorithms by
ensuring that they don't get double-moved. As a result of this
har

[libc++] Fix several double-moves in the code base (#104616)

This patch hardens the "test iterators" we use to test algorithms by
ensuring that they don't get double-moved. As a result of this
hardening, the tests started reporting multiple failures where we would
double-move iterators, which are being fixed in this patch.

In particular:
- Fixed a double-move in pstl.partition
- Add coverage for begin()/end() in subrange tests
- Fix tests for ranges::ends_with and ranges::contains, which were
incorrectly calling begin() twice on the same subrange containing
non-copyable input iterators.

Fixes #100709

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[libc++][test] Avoid non-Standard zero-length arrays (#74183)

Found while running libc++'s test suite with MSVC's STL, where we use
both MSVC's compiler and Clang/LLVM.

MSVC's compiler rejects t

[libc++][test] Avoid non-Standard zero-length arrays (#74183)

Found while running libc++'s test suite with MSVC's STL, where we use
both MSVC's compiler and Clang/LLVM.

MSVC's compiler rejects the non-Standard extension of zero-length
arrays. For conformance, I'm changing these occurrences to
`std::array<int, 0>`.

Many of these files already had `#include <array>`; I'm adding it to the
rest.

I wanted to add `-Wzero-length-array` to
`libcxx/utils/libcxx/test/params.py` to prevent future occurrences, but
it complained about product code :crying_cat_face: :

```
In file included from /home/runner/_work/llvm-project/llvm-project/libcxx/test/std/input.output/iostream.format/input.streams/istream.formatted/istream.formatted.arithmetic/long.pass.cpp:18:
In file included from /home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/istream:170:
In file included from /home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/ostream:172:
In file included from /home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/__system_error/error_code.h:18:
In file included from /home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/__system_error/error_category.h:15:
/home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/string:811:25: error: zero size arrays are an extension [-Werror,-Wzero-length-array]
811 | char __padding_[sizeof(value_type) - 1];
| ^~~~~~~~~~~~~~~~~~~~~~
/home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/string:817:19: note: in instantiation of member class 'std::basic_string<char>::__short' requested here
817 | static_assert(sizeof(__short) == (sizeof(value_type) * (__min_cap + 1)), "__short has an unexpected size.");
| ^
/home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/string:2069:5: note: in instantiation of template class 'std::basic_string<char>' requested here
2069 | _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_LIBCPP_DECLARE, char)
| ^
/home/runner/_work/llvm-project/llvm-project/build/generic-cxx03/include/c++/v1/__string/extern_template_lists.h:31:60: note: expanded from macro '_LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST'
31 | _Func(_LIBCPP_EXPORTED_FROM_ABI basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const*, size_type)) \
| ^
```

I pushed a tiny commit to fix unrelated comment typos, in an attempt to
clear out spurious CI failures.

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[libc++] Implement ranges::ends_with

Reviewed By: #libc, var-const

Differential Revision: https://reviews.llvm.org/D150831