OpenGl_GlCore45 - removed a couple of FFP-related functions introduced by OpenGL 4.5 Compatible Profile, but not Core Profile.
OpenGl_GlFunctions::load() now tries to load a set of functions
from GL_ARB_robustness extension (having ARB suffix) to fill OpenGL 4.5 function table,
and from GL_ARB_indirect_parameters extension to fill missing items in OpenGL 4.6 function table on Intel drivers.
Warning message (trace level) is now reported instead of error in case of fallback usage.
GL_HALF_FLOAT_OES from OpenGL ES 2.0 extension
is now avoided within OpenGL ES 3.0+ context in favor of GL_HALF_FLOAT.
emscripten_webgl_enable_extension() is now called for all extensions
checked by OpenGl_Context::CheckExtension().
So far this doesn't solve any problem, but looks more logical and provisional.
MACOSX_USE_GLX has been renamed to HAVE_XLIB and now configurable on Linux target.
Xw_Window.hxx now export class on non-Linux platforms.
OpenGl_Window now creates an off-screen EGL surface also in case of
window-less desktop setup (e.g. with disabled Xlib on Linux).
Draw_Window - code has been cleaned up.
Class definition has been unified across platforms when possible.
Unusued constructors have been removed.
Internal header files (MainWindow.h, init.h, etc.) have been renamed to .pxx
to avoid their unexpected distribution in "inc".
OpenGl_GlFunctions no more loads unused FFP functions.
OpenGl_GlCoreXX function tables no more defined two hierarchies with and without FFP functions,
and OpenGl_Context::coreXXback fields have been removed.
Introduced OpenGl_Context::core11ffp as more straightforward naming for obsolete FFP function set.
Added new property Graphic3d_Camera::IsZeroToOneDepth() and OpenGl_Caps::useZeroToOneDepth
for activating [0,1] depth range instead of [-1,1] range using glClipControl() within OpenGL 4.5+.
OpenGl_Workspace::Activate() now implicitly disables OpenGl_Caps::ffpEnable when it is unsupported.
OpenGl_AspectsSprite::build() now ignores OpenGl_Caps::pntSpritesDisable when Display Lists are unsupported.
OpenGl_Context now activates Ray-Tracing and arbTboRGB32 for GLES 3.2.
Removed initialization of some uniforms from GLSL code.
Fixed implicit casts within Ray-Tracing shaders.
