✨ add parents to regexp visitor

[connor4312]

Simple change, mostly churn. Adds a readonly array as the second parameter to visitors, containing the parent tree. Reuses the same array internally, pushing and popping nodes, so should have a relatively minimal performance impact.

Fixes https://github.com/mysticatea/regexpp/issues/16

[MichaelDeBoey]

Hi @connor4312!

Since this repo is unmaintained, you might want to re-open this PR in the @eslint-community fork https://github.com/eslint-community/regexpp

For more info about why we created this organization, you can read https://eslint.org/blog/2023/03/announcing-eslint-community-org