Implement support for power events and preventing sleep/suspend in wxGTK

[vadz]

This mainly addresses #23717 but also happens to implement #22396 as a side effect.

[MaartenBent]

I'm getting link errors:

/usr/bin/ld: ../lib/libwx_gtk3u_core-3.3.so.0.0.0: undefined reference to `vtable for wxPowerEvent'
/usr/bin/ld: ../lib/libwx_gtk3u_core-3.3.so.0.0.0: undefined reference to `wxEVT_POWER_SUSPENDED'
/usr/bin/ld: ../lib/libwx_gtk3u_core-3.3.so.0.0.0: undefined reference to `wxEVT_POWER_RESUME'

I think caused by this line. The events are implemented in powercmn.cpp, part of the base library. This doesn't have the __WXGTK__ define. It works when I change it to __UNIX__, though that maybe breaks macOS.

wxWidgets/include/wx/power.h

Line 43 in aa1f7db

#if defined(__WINDOWS__) || defined(__WXGTK__)

[vadz]

Oops, it indeed looks like this can't work (so I wonder how does it manage to work nevertheless for me and in the CI builds too, and what's the difference with your build).

Worse, I'm not sure how to fix it. I think we're going to need to move all wxPowerXXX stuff to core from base. Or we'd need to virtualize it via wxAppTraits, but this would be more complicated and probably not really worth it, or would it be?

[MaartenBent]

Not sure what is different, my build should be the same as CMake builds - Ubuntu 22.04 wxGTK 3. The libraries build fine, it is the samples that fail to link.
I'm ok with moving it to core. But I don't know if there are cases where power events are used in console / base-only applications.

[lanurmi]

It would make perfect sense for a Windows service (using base only) to prevent sleep. However, I'm unsure whether SetThreadExecutionState() actually works with services as the documentation suggests "desktop apps only". Nonetheless, such code can exist and does exist.

[vadz]

It's going to be a lot of work to make this available in MSW console applications and I don't think it's worth it, so for now I've only created #25174. If we really, really need them in base, they could be virtualized later but, again, I just don't think it's worth investing time into this.