Reimplent soft access restriction for members prefixed with _

Author: Lazy-Rabbit-2001

modules/gdscript/gdscript_warning.h

@@ -89,6 +89,8 @@ class GDScriptWarning {
 		NATIVE_METHOD_OVERRIDE, // The script method overrides a native one, this may not work as intended.
 		GET_NODE_DEFAULT_WITHOUT_ONREADY, // A class variable uses `get_node()` (or the `$` notation) as its default value, but does not use the @onready annotation.
 		ONREADY_WITH_EXPORT, // The `@onready` annotation will set the value after `@export` which is likely not intended.
+		ACCESS_PRIVATE_MEMBER, // Accessing a private member from external places. E.g. accessing an `_`-prefixed member from other classes that are not derived from the class where the member is defined.
+		CALL_PRIVATE_METHOD, // Calling a private method from external places. E.g. calling an `_`-prefixed method from other classes that are not derived from the class where the method is defined.
 #ifndef DISABLE_DEPRECATED
 		PROPERTY_USED_AS_FUNCTION, // Function not found, but there's a property with the same name.
 		CONSTANT_USED_AS_FUNCTION, // Function not found, but there's a constant with the same name.
@@ -146,6 +148,8 @@ class GDScriptWarning {
 		ERROR, // NATIVE_METHOD_OVERRIDE // May not work as expected.
 		ERROR, // GET_NODE_DEFAULT_WITHOUT_ONREADY // May not work as expected.
 		ERROR, // ONREADY_WITH_EXPORT // May not work as expected.
+		WARN, // ACCESS_PRIVATE_MEMBER
+		WARN, // CALL_PRIVATE_METHOD
 #ifndef DISABLE_DEPRECATED
 		WARN, // PROPERTY_USED_AS_FUNCTION
 		WARN, // CONSTANT_USED_AS_FUNCTION