Native support for UI Dark Mode

[vit9696]

Apparently there is white text on white background in some places:

[yeggor]

I just now noticed that this has already been discussed. Do you think this solves the problem with protected ranges colors: https://github.com/LongSoft/UEFITool/pull/293?

[NikolajSchlej]

Support for macOS dark mode had been recently added to Qt6, but had not been backported to Qt5 in any way, so we should start using Qt6 (but remain compatible with the last Qt build under LGPLv2.1 - 5.6.3, with some minor UI issues if needed) and get that for free.

• [x] add static Qt 6.4.2 x64 UEFITool build for Windows
• [x] switch to static Qt 6.4.2 universal build for macOS

@yeggor also showed that darkX colors are much nicer-looking in dark mode in #293, but I'd like to detect both Aqua and Dark modes, and switching between them dynamically.

• [x] detect the current mode dynamically, adjust BootGuard marking colors to suit the current mode (Windows)
• [x] detect the current mode dynamically, adjust BootGuard marking colors to suit the current mode (macOS)

[NikolajSchlej]

Got Windows 10+ dark mode working as expected, no overrides required:

[NikolajSchlej]

Now detection of dark mode and setting colors also works in macOS:

[NikolajSchlej]

Done, the current CI/CD pipeline can successfully generate Qt-6.4.2-based builds for both macOS and Windows, and uses a native installed Qt5/6 on Linux. I consider this issue to be resolved, please open another one if UI Dark Mode doesn't work for you in some way.

[NikolajSchlej]

Confirmed macOS way to determine UI dark mode to work in Linux, enabled it there.