Improve Win32 darkmode and fix title bar's context menu

[Pixelsuft]

Description

Use hidden uxtheme.dll and user32.dll functions for darkmode instead of using DwmSetWindowAttribute.
Fixes context menu on title bar.

Notes

I couldn't find function to get Windows build number so I import RtlGetVersion from ntdll to get it.

Existing Issue(s)

#11535

[slouken]

This can be replaced with GetModuleHandle() and GetProcAddress() if you want to avoid a separate load.

[slouken]

SDL style is:

if (true) {
    statement;
} else {
    statement;
}

[slouken]

Please add blank lines between declarations.

[slouken]

I'm not thrilled about using undocumented functions to implement dark mode, but other than that, this looks good to me.

@icculus, thoughts?

[icculus]

I'm not thrilled about using undocumented functions

Especially because we're looking them up by ordinal instead of symbol name! Undocumentedness aside, are these numbers likely to change in later builds?

[Pixelsuft]

I'm not thrilled about using undocumented functions

Especially because we're looking them up by ordinal instead of symbol name! Undocumentedness aside, are these numbers likely to change in later builds?

Some functions were changed/added only in some subsequent win10 builds after dark mode appeared first, and then they haven't been changing for a long time. I don't think microsoft will change them for compatibility reasons.

[icculus]

I'm fine with adding this, but we probably need some switch to turn this off in case a future build of Windows starts making this crash in the field.

[Pixelsuft]

I'm fine with adding this, but we probably need some switch to turn this off in case a future build of Windows starts making this crash in the field.

I agree, but I don't think I will be able to implement it.

[Pixelsuft]

Just found some apps already use hidden uxtheme functions:
MPV Player
System Informer
Notepad++ (likely modified darkmode example app code)
Chromium

[bitRAKE]

Another option is to get the build number from KUSER_SHARED_DATA.NtBuildNumber. Not only is it mapped into all processes, but it's the same on 32/64-bit. Reduces to two instructions to exclude earlier builds.

Edit: I've overstated - KUSER_SHARED_DATA.NtBuildNumber was defined with Win10. This means excluding KUSER_SHARED_DATA.NtMajorVersion less than 10 prior to examining the build number. Good back to NT4 that way.