Add EGL bindings for surfaceless contexts

[onox]

Add EGL bindings to create a (surfaceless) context for headless rendering on the following platforms:

• Wayland
• Mesa GBM
• Device
• Add Orka.Contexts.EGL package

[onox]

EGL bindings for surfaceless contexts are working. Need to figure out though how to use it via Orka.Contexts. Currently you make a context current by using a constructed Window:

Library : constant Orka.Contexts.Library'Class
  := Orka.Windows.GLFW.Initialize (Major => 4, Minor => 2);

Window : aliased Orka.Windows.Window'Class
  := Library.Create_Window (Width => 500, Height => 500, Resizable => False);

Context : constant Orka.Contexts.Context'Class := Window.Context;
pragma Unreferenced (Context);

The context is created by GLFW in Create_Window and made current via the Context constant (RAII). This is kinda backwards since you surfaces are optional if an EGLDisplay supports surfaceless contexts. I would prefer to have something like this:

Context : Orka.Contexts.Context'Class
  := Orka.Windows.GLFW.Create_Context (Version => (4, 2), Flags => (Debug => True, others => False));

Window : aliased Orka.Windows.Window'Class
  := Context.Create_Window (Width => 500, Height => 500, Resizable => False);

Without a window, a context can be created and made current via:

Context : Orka.Contexts.Context'Class
  := Orka.Windows.EGL.Create_Context (Surfaceless, Version => (4, 2), Flags => (Debug => True, others => False));