Allow DEBUG_ENABLED to be toggled independently of TOOLS_ENABLED

[lyuma]

Makes debugging of unusual release-only issues such as godotengine/godot-cpp#842 easier from an editor build without needing to make a separate template build to reproduce them.

This is mostly useful for target=editor since there is at present no way to make a "release editor".

For example, these will build debug builds without the DEBUG_ENABLED macro (perhaps to allow debugging of release-specific crashes)

scons target=editor debug_features=no
scons target=template_debug debug_features=no

or build a release build with optimizations, but with DEBUG_ENABLED turned on.

scons target=template_release debug_features=yes

debug_features defaults to auto which is yes for target=template_release and no for target=editor or target=template_debug

There could be usecases for building a debuggable template, but it's unclear what the difference is between my proposed target=template_debug debug_features=no and target=template_release optimization=debug debug_symbols=yes

I'd be open to adding target=editor_release instead if it makes more sense.

Regarding the changes in the PR, they are to make checks consistent across the codebase.

As one example, ClassDB metadata and argument info are enabled when DEBUG_METHODS_ENABLED (which means the same thing as DEBUG_ENABLED, I think?), so it makes sense to permit --dump-gdextension-api when DEBUG_ENABLED.