Add ANGLE support for linux builds

[LucasGGamerM]

Is your feature request related to a problem? Please describe.
I have an intel hd 3000 gpu in one of my laptops, and according to the readme, using ANGLE with the swiftshader backend might make it support newer versions of OpenGL ES (it currently uses version 3.0 from mesa), and it seems that soon version 3.1 will be the new requirement.

Describe the solution you'd like
A way (just documentation would be fine) to swap the required .so files to get ANGLE working (and possibly get OpenGL ES 3.1 support going).

Describe alternatives you've considered
None

Additional context
Please correct me if I have spoken anything that is untrue, and thank you a lot for your work!

[ChristopherHX]

I do not see any advantage over just setting your env variable LIBGL_ALWAYS_SOFTWARE to 1 on linux.

Both fallbacks do not give your intel hd 3000 gpu support for newer versions of OpenGL ES.

• Very huge Performance drop is expected
• CPU needs to do everything
• Reduced FPS stability

You are better of getting newer Hardware.