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/sdfgi_debug.glsl

@@ -2,7 +2,7 @@
 
 #version 450
 
-VERSION_DEFINES
+#VERSION_DEFINES
 
 layout(local_size_x = 8, local_size_y = 8, local_size_z = 1) in;