gh-152433: Windows: fix errors in sys.getwindowsversion() for UWP build

[thexai]

Fixes errors in sys.getwindowsversion() only for UWP build, not changes behavior in Windows desktop.

• Issue: Windows: improve compatibility to build for UWP / Xbox #152433

[thexai]

For more context, the actual issue with sys.getwindowsversion() is that return incorrect value in recent Windows 11 versions:

e.g: in Windows 11 25H2 return 10.0.26100 instead of correct 10.0.26200.

(but not directly observable because only is used as second fallback on platform module)

With this change, it will be possible use sys.getwindowsversion() as the first fallback (after WMI) and will also be compatible with UWP.

In UWP, it would be the primary method because WMI is not available and subprocess "cmd ver" is also not available.

Related to #129294

[thexai]

Updated with alternative fix:

    // Obtain the build number from Windows registry in case of Windows 10/11
    if (realMajor == 10 && realMinor == 0) {
        wchar_t currentBuild[32] = {0};
        DWORD len = sizeof(currentBuild);
        if (ERROR_SUCCESS == RegGetValueW(HKEY_LOCAL_MACHINE, REG_CURRENT_VERSION, L"CurrentBuild",
            RRF_RT_REG_SZ, NULL, &currentBuild, &len))
        {
            realBuild = _wtol(currentBuild);
        }
    }

[zooba]

the point of this API is to find out what OS features are available, and if you're under compatibility shims, they may not be. In that case, getting the "real" version is going to be a lie.

So the right answer to "what version should I assume is running" is the one that GetVersion returns.

[thexai]

Okay, we'll take it one step at a time...

[thexai]

PR updated: only fixes things in UWP build, not touches anything in regular Windows desktop build.

[MatejKafka]

Updated with alternative fix:

Is that Registry key actually documented? If not, using it directly seems at least as bad as using RtlGetVersion (i.e., not very, in my opinion, but if RtlGetVersion is considered problematic, I don't really see why touching Registry directly would be better).