Bitmask ints can't be converted to strings

While we do have an auto cast function that handles an int to string conversion, bitmask ints use a "bitmask" subcategory which thwarts are ability to find the cast function.

1. Open Issue4_BP
2. Drag connection from Int Var to In String of the first print node.
3. Observe that it automatically creates an int->string conversion node.
4. Drag connection from Return Value of the Make Bitmask node to In String of the second print node.
5. Observe that the connection is disallowed and no conversion node is created.
6. Expected behavior: a conversion node should be created automatically, just like with the getter node.