Ports the Ruby regex library to C++/ECMAScript (`std::regex` default dialect):
- `cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll`: ECMAScript-adapted parser over `StringLiteral`
- `cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll`: tree view implementing `RegexTreeViewSig`
- `cpp/ql/lib/qlpack.yml`: add `codeql/regex` dependency (already present)
- `cpp/ql/test/library-tests/regex/`: hermetic test corpus (test.cpp with std:: stubs), parse.ql, regexp.ql, RegExpConfig.qll
- `cpp/ql/lib/change-notes/released/12.1.0.md`: minorAnalysis change note
Note: .expected files are placeholders; run `codeql test run --accept` after database generation to populate them.
