vgui_support: initial vgui2 support

[kungfulon]

Counter-Strike 1.6 is loadable and playable with VGUI menus disabled. Currently no menu rendering is implemented and input is disabled.

The code will be gradually updated to implement rendering and input.

[a1batross]

That could be annoying but what if we generate headers based on DWARF data rather than using Source SDK ones? For example, pdwtags/pahole from dwarves utils can generate C++ code from debug info.

I did this for VGUI1 (it's not published yet) and filesystem_stdio. At least, we're not bringing unneeded proprietary headers this way.

[kungfulon]

Actually, the headers in vgui2-dev are generated from running pahole as well, I just took time to clean it up and make it looks like source sdk headers. If you want any change to avoid licensing problems, please tell me.

[a1batross]

The Valve interface file looks suspicious. :)

In filesystem_stdio I just wrote CreateInterface export myself, than relying on Source SDK macros.

[kungfulon]

Oh, that one I took from HLSDK indeed. I can change it to self-made CreateInterface.

[kungfulon]

BTW VGUI2 need to load libraries and get exports from them, so I think these functions should be exposed to vguiapi_t, if we want to get rid of valve interface.cpp and interface.h.

[kungfulon]

OK, I made some changes to avoid using valve interface, only keeping basic types got from DWARF.

Moving forward I'll also update GPL license header to vgui2-dev.

[kungfulon]

Updated vgui2-dev to state that the headers and sources are reverse engineered using DWARF information and added GPL licensing header.

[a1batross]

I'm mostly fine with these changes, for now it's all stubs and require reworking engine API anyway (API is also not forward and backward compatible).

This will be merged as soon as API would be redone. I can do it myself, as soon as I will return from vacation OR you can do it yourself just in the same style like engine's RefAPI, RenderAPI or FS API.

[a1batross]

Oh, and since it uses "auto" which is C++11 feature, it would be nice to have override on the vgui2 interface methods.