Add validRegexPattern assertions

[zlodes]

Why?

1. PHP functions working with regex (preg_match, preg_replace, etc.) work in legacy way — they just return false instead of throwing exception.
2. The way to check if the string is regex is quite hacky, so, would be great to hide the check implementation somewhere.

References

1. https://stackoverflow.com/a/8825096/3578207

[zlodes]

I see that some tests failed. Fixing. 🤔

[zlodes]

@shadowhand Hello mate!

As I can see, the latest release of the package was in 2022. Is there any plans for the next release?