Matching `(` and `)` in a regexp matcher requires escaping

[lucacasonato]

Fails, even though it's valid:

const pattern = new URLPattern({ pathname: '/([()])' });
Uncaught TypeError: tokenizer error: invalid regex: nested groups must start with ? (at char 1)

OK:

const pattern = new URLPattern({ pathname: '/([\\(\\)])' });

This is because while tokenizing the pattern, we think the second ( is a nested group rather than just a char in a regexp character class.

Fixing this will make the tokenizer more complicated. Is it worth it?