[NO SQUASH] Non-SDL: Add opengl3 support

[SmallJoker]

video_driver = opengl3 support for the non-SDL Linux and Win32 Irrlicht device.

Benefits:

• Less code duplication (of stub functions)
• Alternative access to OpenGL 3 without the SDL2 dependency
• Minimal amount of additional code.
• ????

The change GL_VENDOR -> GL_RENDERER was done because latter does provide more helpful information about the video card that is being used. See debug_log_level = info + debug.txt for comparison.

• Before: glxinfo | grep "OpenGL vendor string" (vendor name only)
• Now: glxinfo | grep "OpenGL renderer string" (more detailed graphics card information)

To do

This PR is Ready for Review.

How to test

1. Compile with USE_SDL2=0 and ENABLE_OPENGL3=1
2. See window title
3. See debug.txt
4. Shaders must work
5. Dynamic shadows should work properly
6. ??

[sfan5]

Rebase needed.
Considering we are hoping to stay with SDL for real this time you may choose that the effort is not worth it and close the PR.

[SmallJoker]

The rebase was trivial. I am continuing this until SDL is mandatory on all platforms.

[sfan5]

can you turn this into a real check?
https://github.com/minetest/minetest/blob/0c3117f9b32624955846314ebf87f757d124184f/irr/src/OpenGL3/Driver.cpp#L37-L38

side note: this only currently works because the the opengl3 driver doesn't (yet) use the core profile, but runs in the compatibility profile.
if this wasn't the case the GLX and WGL plumbing code would need actual changes to make this work.

[sfan5]

doesn't break anything. shadows work on gl3.