Fix compatibility with PHP 8 after "Treat namespaced names as single token" RFC

[ondrejmirtes]

Version: nette/utils master on PHP 8 nightly

This RFC breaks Reflection class: https://wiki.php.net/rfc/namespaced_names_as_token
This is how the tests fail: https://github.com/ondrejmirtes/utils/runs/924516761?check_suite_focus=true#step:5:54

This is a proof-of-concept fix: ondrejmirtes@e55a8da

I'd send a PR but there are other build failures I'm not sure how you want fixed. Feel free to check out my branch: https://github.com/ondrejmirtes/utils/commits/php-8

[dg]

Merged, thanks