Add integer posmod and rename default arg names

"posmod" is the integer version of "fposmod". We do not need a "mod" because of the % operator.

I changed the default arg names from "x" and "y" to "a" and "b" because they are not coordinates. I also changed pow's arg names to "base" and "exp". Also, I reorganized the code in the VS built-in funcs switch statement.

modules/visual_script/visual_script_builtin_funcs.h

@@ -104,6 +104,7 @@ public:
 		BYTES_TO_VAR,
 		COLORN,
 		MATH_SMOOTHSTEP,
+		MATH_POSMOD,
 		FUNC_MAX
 	};