Multibyte support for STR::snake/kebab methods

[zoryamba]

Str::snake still use ucwords which doesn't support multibyte strings.
It's the last use of ucwords in Str class. It was removed previously from Str::studly in #40468
This seems to be an obvious bug for me, but PR to fix this (#51626) was closed with "No plans" reasoning.

So I want to raise a discussion, should Str::snake work correct with multibyte strings?

Actual behavior:

Str::snake('ÖffentlicheÜberraschungen'); // öffentlicheüberraschungen
Str::snake('ŻółtaŁódka') // żółtałódka

Expected behavior:

Str::snake('ÖffentlicheÜberraschungen'); // öffentliche_überraschungen
Str::snake('ŻółtaŁódka') // żółta_łódka

[shaedrich]

Yeah, multibyte support would be the standard. Having non-multibyte strings with multibyte support has no disadvantages to my knowledge, so it's hard to argue against this accept for laziness in terms of implementation maybe, but this is a very weak argument.