feat: Custom Vertex Attributes

[emadurandal]

This feature is ...

• Implement the System for Custom Vertex Attribute Layout like:
  • VertexAttributeSlot 0: "Position.X, Position.Y, Position.Z, Texcoord.X"
  • VertexAttributeSlot 1: "Normal.X, Normal.Y, Normal.Z, Texcoord.Y"
• Add the shader system which converts their custom layout vertex attributes to each standard vertex attribute (Position, Normal, Texcoord, etc...)
• Add the "CustomVertexAttribute" class, which has functionalities of view / copy to a target vertex attributes layout from an original vertex attributes layout.

The shader system converts this:

attribute vec4 a_customAttribute0;
attribute vec4 a_customAttribute1;

to

vec3 v_position = a_customAttribute0.xyz;
vec3 v_normal = a_customAttribute1.xyz;
vec2 v_texcoord = vec2(a_customAttribute0.w, a_customAttribute1.w);