Implement a rule to lint enum entry name

[yukukotani]

Resolve #635

Implement an experimental rule to lint enum entry name.
This rule enforces enum entry names to

1. contains no lower case letter if it contains under score.
2. starts with upper case if it contains lower case letter.

So, "ENTRY_NAME" and "EntryName" are valid, "Entry_Name", "entry_name" and "entryName" are invalid.

Currently auto-format will convert entry name to all upper case, but this behavior is highly debatable.

Before format

enum class FirstEnum {
    enum_entry
}
enum class SecondEnum {
    entry
}

formatted

enum class FirstEnum {
    ENUM_ENTRY
}
enum class SecondEnum {
    ENTRY
}

[yukukotani]

I forgot an important thing. This format might causes compile error because enum entry identifier will be changed.
Maybe formatting should be disabled and just lint.

[Tapchicoma]

I would propose to disable formatting for now.

Generally it is interesting question how to handle such cases that makes code non-compilable. Maybe via some additional configuration flag - allowBreakingFormatting 🤔

[shashachu]

Agree that we should disable formatting if it could cause compile errors.

[yukukotani]

@Tapchicoma @shashachu
Thank you for your feedback. I disabled formatting for now, but leave formatting logic.
Also, created an issue #656 about supporting allowBreakingFormatting option.

[Tapchicoma]

Thank you for fixing this 👍