`<filesystem>`: std::filesystem::relative not accounting for drive letter case

Describe the bug

std::filesystem::relative does not take into account drive letter capitalization rules. In Windows, the drive letter C: or c: are equivalent. However std:filesystem::relative() does not respect this rule.

Test case

#include <filesystem>
#include <iostream>

int main()
{
    std::filesystem::path a("C:\\a\\b\\path");
    std::filesystem::path b("c:\\a\\x\\y\\file");

    std::cout << "Relative between a and b is " << std::filesystem::relative(a, b) << "\n";
}

Expected behavior

I would expect this function to return "Relative between a and b is ..\..\x\y\file which is the output if a use the windows API

#include <windows.h>
#include <iostream>
#include "Shlwapi.h"

void main(void)
{
    char szOut[MAX_PATH] = "";
    char szFrom[ ] = "C:\\a\\b\\path";
    char szTo[ ] = "c:\\a\\x\\y\\file";

    std::cout  <<  "The relative path is relative from: ";
    std::cout  <<  szFrom;
    std::cout  <<  "\n";

    std::cout  <<  "The relative path is relative to: ";
    std::cout  <<  szTo;
    std::cout  <<  "\n";

    PathRelativePathTo(szOut,
                       szFrom,
                       FILE_ATTRIBUTE_DIRECTORY,
                       szTo,
                       FILE_ATTRIBUTE_NORMAL);

    std::cout  <<  "The relative path is: ";
    std::cout  <<  szOut;
    std::cout  <<  "\n";
}

Output from above is

The relative path is relative from: C:\a\b\path
The relative path is relative to: c:\a\x\y\file
The relative path is: ..\..\x\y\file

Start by reproducing the Windows case with std::filesystem::relative using the paths shown, then locate the implementation and tests for that entry point in the STL repository. Done means drive-letter case is treated equivalently and the result matches the expected ....\x\y\file path.