Improve variable names

[szepeviktor]

Currently there are ~300 lines with names like key, value, data. Please consider using informative variable names. source

// For example
protected function setDomain(string $value, bool $viaAttribute = false): void {}
protected function setDomain(string $domainName, bool $viaAttribute = false): void {}

[otsch]

Those occurrences don't have to be bad per se. For example some occurrences are even dictated by PSR interfaces, like in the CacheInterface of PSR-16, which absolutely make sense. As I don't really see a big "issue" here, I'll close this. Send a PR if you like to improve some particular variable names.