Depsgraph: Add generic parameters evaluation operation code

Currently unused, but the idea is to use this code instead of placeholder
operation code followed by string comparison.

source/blender/depsgraph/intern/depsgraph_type_defines.cc

@@ -100,6 +100,7 @@ static const char *stringify_opcode(eDepsOperation_Code opcode)
 #define STRINGIFY_OPCODE(name) case DEG_OPCODE_##name: return #name
 		/* Generic Operations. */
 		STRINGIFY_OPCODE(OPERATION);
+		STRINGIFY_OPCODE(PARAMETERS_EVAL);
 		STRINGIFY_OPCODE(PLACEHOLDER);
 		/* Animation, Drivers, etc. */
 		STRINGIFY_OPCODE(ANIMATION);

source/blender/depsgraph/intern/depsgraph_types.h

@@ -141,6 +141,9 @@ typedef enum eDepsOperation_Code {
 	/* Placeholder for operations which don't need special mention */
 	DEG_OPCODE_OPERATION = 0,
 
+	/* Generic parameters evaluation. */
+	DEG_OPCODE_PARAMETERS_EVAL,
+
 	// XXX: Placeholder while porting depsgraph code
 	DEG_OPCODE_PLACEHOLDER,