Make `randbase` member protected in `RandomNumberGenerator`
Make `randbase` member protected in `RandomNumberGenerator`

Allows to extend `RandomNumberGenerator` via C++ modules.

(cherry picked from commit 1923f0d3027ce92e4d42f0436d90beea0c0dee3e)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot