0028912: Visualization, TKOpenGl - multi-texture support

Graphic3d_AspectFillArea3d now stores array of textures.
Graphic3d_TextureParams stores texture unit for mapping texture.

OpenGl_Context::BindTextures() - context now manages the set of active textures.
Related code has been removed from OpenGl_Workspace.

OpenGl_Sampler has been extended to hold texture parameters structure.
OpenGl_Texture now holds OpenGl_Sampler instance as class field.
OpenGl_Texture inherits new class OpenGl_NamedResource and holds
texture identifier used for sharing resource in OpenGl_Context.

OpenGl_RaytraceGeometry now creates bindless textures taking
Sampler object directly from OpenGl_Texture.
OpenGl_Context::BindTextures() automatically recreates immutable
Sampler Object on texture parameters change.

Declared new structure OpenGl_ArbSamplerObject for platform-neutral
usage of related functionality.
Related functions are now loaded within OpenGL ES 3.0+.

Declarations.glsl - occActiveSampler has been renamed to occSampler0
with aliases occSamplerBaseColor (main) and occActiveSampler (for compatibility).
Additional texture samplers should be declared explicitly
within specific GLSL program as occSampler1, occSampler2, etc.

AIS_Shape and AIS_ColoredShape now computes Shaded presentation
with UV coordinates if texture mapping is enabled in Drawer.

vshaderprog now accepts Shader source code as parameter.

src/OpenGl/OpenGl_View.hxx

@@ -332,7 +332,7 @@ public:
   const Handle(OpenGl_Window) GlWindow() const { return myWindow; }
 
   //! Returns OpenGL environment map.
-  const Handle(OpenGl_Texture)& GlTextureEnv() const { return myTextureEnv; }
+  const Handle(OpenGl_TextureSet)& GlTextureEnv() const { return myTextureEnv; }
 
   //! Returns selector for BVH tree, providing a possibility to store information
   //! about current view volume and to detect which objects are overlapping it.
@@ -503,7 +503,7 @@ protected:
 
   OpenGl_GraduatedTrihedron myGraduatedTrihedron;
 
-  Handle(OpenGl_Texture) myTextureEnv;
+  Handle(OpenGl_TextureSet) myTextureEnv;
 
   //! Framebuffers for OpenGL output.
   Handle(OpenGl_FrameBuffer) myOpenGlFBO;
@@ -614,30 +614,6 @@ protected: //! @name data types related to ray-tracing
     OpenGl_RT_NbVariables // special field
   };
 
-  //! Defines OpenGL texture samplers.
-  enum ShaderSamplerNames
-  {
-    OpenGl_RT_EnvironmentMapTexture = 0,
-
-    OpenGl_RT_SceneNodeInfoTexture  = 1,
-    OpenGl_RT_SceneMinPointTexture  = 2,
-    OpenGl_RT_SceneMaxPointTexture  = 3,
-    OpenGl_RT_SceneTransformTexture = 4,
-
-    OpenGl_RT_GeometryVertexTexture = 5,
-    OpenGl_RT_GeometryNormalTexture = 6,
-    OpenGl_RT_GeometryTexCrdTexture = 7,
-    OpenGl_RT_GeometryTriangTexture = 8,
-
-    OpenGl_RT_RaytraceMaterialTexture = 9,
-    OpenGl_RT_RaytraceLightSrcTexture = 10,
-
-    OpenGl_RT_FsaaInputTexture = 11,
-    OpenGl_RT_PrevAccumTexture = 12,
-
-    OpenGl_RT_RaytraceDepthTexture = 13
-  };
-
   //! Defines OpenGL image samplers.
   enum ShaderImageNames
   {