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().

modules/lightmapper_rd/lm_compute.glsl

@@ -10,7 +10,7 @@ light_probes = "#define MODE_LIGHT_PROBES";
 
 #version 450
 
-VERSION_DEFINES
+#VERSION_DEFINES
 
 // One 2D local group focusing in one layer at a time, though all
 // in parallel (no barriers) makes more sense than a 3D local group