VL v2.2 PR

[MicBosi]

• Adds GLSLComputeShader
• Added OpenGLFunctions object wrapping all GL functions
• Every OpenGLContext now has access to OpenGLFunctions object initialized with all the available functions according to the current GL context capabilities
• Upgraded GL headers to latest 4.6
• Revamped GL headers and GL function handling: GL function list generated directly from latest GL headers via scripts
• Removed legacy GLES code
• Removed legacy VL_... wrapper functions for GL functions coming from different extensions