Fix wrongly used value in enum handling in the settings menu

[Wartori54]

The default handling of Enum as a setting mixed the value and the index of the value, causing enums which do not have the values auto assigned in c# to misbehave.
This was first reported with an enum like following:

public enum MyEnum {
    Option1 = 0x1,
    Option2 = 0xff,
}

public MyEnum MyEnumSetting { get; set; } = MyEnum.Option2;

where the settings menu showed Option1 right after adding the setting to the class. This is due to mixing an internal index with the enum value.
Furthermore, it also saved the wrong values in the yaml, due to it using the internal index, rather than the proper value associated with the selected enum value.

[microlith57]

👍

[microlith57]

👍

[wuke32767]

should we .distinct() it first?

[Wartori54]

Depends on how we want to handle that case. I'd say it is not really beneficial to eliminate duplicate values since having indistinguishable enum values does not make much sense in an enum for configuration. Thus we shouldn't handle that case.