<codecvt>: Using codecvt_utf16 with wofstream results in malformed UTF16 output

[BillyONeal]

Describe the bug
Newline translation that the CRT is doing on our behalf is transforming \n into \r\n, but this isn't being reflected to the codecvt facet.

Command-line test case
STL version (git commit or Visual Studio version): Visual Studio 2019 version 16.4

C:\Users\bion\Desktop>type test.cpp
#define _SILENCE_CXX17_CODECVT_HEADER_DEPRECATION_WARNING
#include <assert.h>
#include <codecvt>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string_view>

using namespace std::string_view_literals;

int main() {
  const auto target = std::filesystem::temp_directory_path() / "wide.dat"sv;
  std::cout << target << "\n" << std::flush;
  {
    std::wofstream wide(target);
    auto fac =
        new std::codecvt_utf16<wchar_t, 0x10ffff,
                               std::codecvt_mode(std::consume_header |
                                                 std::generate_header)>();
    std::locale uni16(wide.getloc(), fac);
    wide.imbue(uni16);
    wide << "Some text\n";
  }

  {
    std::string actual;
    {
      std::ifstream i(target, std::ios_base::in | std::ios_base::binary);
      std::stringstream s;
      s << i.rdbuf();
      actual = std::move(s).str();
    }
    assert(actual == "\xFE\xFF\0S\0o\0m\0e\0 \0t\0e\0x\0t\0\r\0\n"sv);
  }

  return 0;
}

C:\Users\bion\Desktop>cl /EHsc /W4 /WX /std:c++latest /nologo .\test.cpp
test.cpp

C:\Users\bion\Desktop>.\test.exe
"C:\\Users\\bion\\AppData\\Local\\Temp\\wide.dat"
Assertion failed: actual == "\xFE\xFF\0S\0o\0m\0e\0 \0t\0e\0x\0t\0\r\0\n"sv, file .\test.cpp, line 34

C:\Users\bion\Desktop>

Note the incorrect 0x0D 0x0A terminating the file:

This is a dual of Microsoft-internal VSO-208747 / AB#208747.