Remove qt5 support and fix kf6

[Gigas002]

This PR is arguable, and it's completely OK to banish it from existence if you don't feel it fits the project well

It does these things:

• remove qt5 vars/code, so that we support only compilation with qt6
• fixes the KDE_SUPPORT for Plasma 6 (which is dependent on qt6, so I don't see the point in supporting EOL qt5)
• fixes some nasty gcc 14 warnings
• Exiv2::enableBMFF(true); is deprecated and seems not needed anymore

gcc warnings stuff may be backported to a current version, that utilizes the qt5, but the kf6 fixes aren't, afaik

Also a note about mainwindow.cpp changes for kf6: the KWindowEffects::enableBlurBehind now takes QWindow instead of winId, and while the applyWindowedBackground was being called applyWindowedBackground with kf5 wasn't a bad thing, now it crashes, because the window not exists on a first call. That's why the check here is needed, though it's a bit nasty

[eddiezato]

FYI, with the move to Qt6, the qtraw plugin will stop working as it is seems abandoned by the author and needs to be fixed for Qt6.

[Gigas002]

Thanks for info. Does this actually fails for you to open raw files without it? I can open DNG just fine

[eddiezato]

Yeah. It's failing. But I'm on Windows, not sure about Linux.

[Gigas002]

I think that plugin builds with qt6, would be glad if someone could test it on windows. I only needed to change one line in main.cpp to build it on linux:

QImageIOPlugin::Capabilities
RawPlugin::capabilities(QIODevice *device, const QByteArray &format) const
{
    if (keys().contains(format) ||
        format == "tif" ||
        format == "tiff")
        return Capabilities(CanRead);
    if (!format.isEmpty())
-        return 0;
+        return {};

    Capabilities cap;
    if (device->isReadable() && RawIOHandler::canRead(device))
        cap |= CanRead;
    return cap;
}

[eddiezato]

It builds successfully on windows. But qimgv still won't display raw files with it.