GDScript: Add support for variadic functions

modules/gdscript/tests/scripts/parser/errors/variadic_func_params_after_rest.gd

@@ -0,0 +1,5 @@
+func f(...args, extra_arg):
+	pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/parser/errors/variadic_func_params_after_rest.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+Cannot have parameters after the rest parameter.

modules/gdscript/tests/scripts/parser/errors/variadic_func_rest_after_rest.gd

@@ -0,0 +1,5 @@
+func f(...args, ...more_args):
+	pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/parser/errors/variadic_func_rest_after_rest.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+Cannot have parameters after the rest parameter.

modules/gdscript/tests/scripts/parser/errors/variadic_func_rest_with_default.gd

@@ -0,0 +1,5 @@
+func f(...args = []):
+	pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/parser/errors/variadic_func_rest_with_default.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+The rest parameter cannot have a default value.

modules/gdscript/tests/scripts/parser/errors/variadic_func_static_init.gd

@@ -0,0 +1,5 @@
+static func _static_init(...args) -> void:
+	pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/parser/errors/variadic_func_static_init.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+Static constructor cannot have parameters.