Support custon names for EnumClass

I need to have an enum for countries, with values like `Mèxico` and just use my enum `Country.mexico` everywhere.

Currently I need to implement a mapper from the string to the enum, and I believe that this could be automatically done if the name of the enums could be customizable and so I can have custom `valueOf` autogenerated too.

# Current
`EnumClass.name` contains the name of the variable itself.

# Expected
I can override name for EnumClass with a custom string.

# Ideas
- Add a variable `name` in the `BuiltValueEnumConst`. that override this.