Add support for nullable enums, and improve standalone facets

[Nytra]

This works, however there is a bit of semi-duplicated code because the handling for this needs to be slightly different from the normal handling of config keys

Also I'm not sure if these work with the standalone facets (haven't tested it yet)

[Nytra]

There are some test keys for this in TooltipConfig that might need to be removed

[Nytra]

I'm pretty sure the last commits broke normal config keys (non-nullable ones)

[Nytra]

I would also like to look at consolidating the enum flags generation since right now there are two methods that do it

[Banane9]

Hmmm, seemed fine when I gave it a quick test, but definitely have a look at it. And yea, consolidating the enum generation would be nice. If you want, you can have a go at creating the "sync bool field with (nullable) enum value" methods that I mentioned in fieldextensions too. They'd basically do what the settings do now.

[Nytra]

The only problem with this now is that you cannot turn off the NONE flag (Flag 0) in the test flag enums. This is likely something wrong in GenerateFlagsEnumFields

edit: actually that might not be a bug, it might just be how bitflags work

[Banane9]

Yea, ANDing a full zero pattern always matches with the zero pattern in the end. Flags don't need a None option in that sense.