[Fix #8683] Make naming cops work with non-ascii characters

[tejasbubane]

Closes #8683

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[marcandre]

Good work, thanks!

[bbatsov]

I was going to say that I'd have this be configurable, as I don't want non-ascii characters in any names for various reasons. I guess you could have that the behaviour you changed was a feature, not a bug. :) Anyways, we can always adjust this later.

[marcandre]

Sure, or there could be a cop for that...
This PR changed the definition of what is camel case vs snake case though, which is a concept that is valid for non-ascii characters.
I doubt there are much cases of unwanted non-ascii characters in codebases though.

[bbatsov]

Well, I've worked on codebases where we had international teams and some people would name stuff in their language (e.g. German or French) instead of English and this caused some confusion and frustration. I can imagine some valid use-cases for non-ascii characters, but not that many of them. :-)