Override for debug_features in SCons and CMake

[enetheru]

@Naros raised that after the recent CMake changes his builds now have the DEBUG_ENABLED flag set.

This is due to using the godot-cpp build target being editor or debug_template.
The CMake scripts now match the SCons scripts, which was not previously the case.

In SCons there is an attribute debug_features which is dependent on the target being either template_debug or editor
this is then used to add DEBUG_ENABLED and DEBUG_METHODS_ENABLED to the CPPDEFINES.

This PR adds a new option to both SCons and CMake, debug_features and GODOTCPP_DEBUG_FEATURES respectively, which when unset uses the existing logic, and allows a user to explcitly enable or disable the debug_features.

This works exactly the same way as the use_hot_reload option.