Refactor GLSL shader compilation

-Used a more consistent set of keywords for the shader
-Remove all harcoded entry points
-Re-wrote the GLSL shader parser, new system is more flexible. Allows any entry point organization.
-Entry point for sky shaders is now sky().
-Entry point for particle shaders is now process().

servers/rendering/renderer_rd/shaders/cluster_render.glsl

@@ -2,7 +2,7 @@
 
 #version 450
 
-VERSION_DEFINES
+#VERSION_DEFINES
 
 layout(location = 0) in vec3 vertex_attrib;
 
@@ -63,7 +63,7 @@ void main() {
 
 #version 450
 
-VERSION_DEFINES
+#VERSION_DEFINES
 
 #if defined(has_GL_KHR_shader_subgroup_ballot) && defined(has_GL_KHR_shader_subgroup_arithmetic) && defined(has_GL_KHR_shader_subgroup_vote)