[BUG] Invalid enum var names are generated by multi-byte characters

[shmakovalexey]

Description

It's another solution for ISSUE-893

The project [swagger-codegen] (https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultCodegen.java#L324) contains a check for the uniqueness of names, as a result, when using multibyte characters, instead of a list of characters "_", classes are obtained without compilation errors. I think we need to do the same.

In a perfect world, it's the swagger description provider that should add the "x-enum-names" parameter, but in the real world it's very hard to get an external organization to modify their file. Thus, it will be very useful if third-party files are converted into classes that compile without errors.