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/shader_compiler_rd.h

@@ -38,7 +38,16 @@
 
 class ShaderCompilerRD {
 public:
+	enum Stage {
+		STAGE_VERTEX,
+		STAGE_FRAGMENT,
+		STAGE_COMPUTE,
+		STAGE_MAX
+	};
+
 	struct IdentifierActions {
+		Map<StringName, Stage> entry_point_stages;
+
 		Map<StringName, Pair<int *, int>> render_mode_values;
 		Map<StringName, bool *> render_mode_flags;
 		Map<StringName, bool *> usage_flag_pointers;
@@ -63,13 +72,9 @@ public:
 		Vector<uint32_t> uniform_offsets;
 		uint32_t uniform_total_size;
 		String uniforms;
-		String vertex_global;
-		String vertex;
-		String fragment_global;
-		String fragment;
-		String light;
-		String compute_global;
-		String compute;
+		String stage_globals[STAGE_MAX];
+
+		Map<String, String> code;
 
 		bool uses_global_textures;
 		bool uses_fragment_time;
@@ -103,10 +108,6 @@ private:
 	const ShaderLanguage::ShaderNode *shader;
 	const ShaderLanguage::FunctionNode *function;
 	StringName current_func_name;
-	StringName vertex_name;
-	StringName fragment_name;
-	StringName light_name;
-	StringName compute_name;
 	StringName time_name;
 	Set<StringName> texture_functions;