Fix QtWebEngine to work with gtkplatform

[rburchell]

... and perhaps more platforms in general, by upstreaming a patch removing the hardcoded list of supported platforms.

There's no sense in having this list I think. If it gets a pointer back for eglcontext, it should try to use it - nothing else in Qt has such a hardcoded list of supported platforms.

[rburchell]

[this is a mass update]

This is polite notice that gtkplatform is effectively end of life. Due to this, I've decided to archive the project.

I (and I think, the other contributors) have not been using it in quite some time, and I don't see that situation changing any time soon. In addition, none of us really have the time that it takes to do what it takes to keep the lights on, and this situation is going to get a lot harder soon with the impending arrival of Qt 6 and gtk 4 on the horizon.

Should anyone wish to take it over, you have my blessing to do so :)