chore: use substring for consistency

perf: avoid matchReg on common character class escape

annex-b: \ can be ClassAtomNoDash if followed by c

fix: descend ClassStringDisjunction from ClassSetOperand

fix: only ±lookbehind is quantifiable in annexB

fix: unicode escape sequence within RegExpIdentifier is always in uni…

fix: allow empty disabling flags

fix: throw invalid error at the pos of flag

polish: throw for invalid modifiers in the middle

supress regexp/use-ignore-case errors

fix: throw on unescaped class set reserved double punctuator

fix: throw on unescaped class set reserved double punctuator

Add test

suppress no-unused-vars errors

Update Unicode to 16.0.0

Prepare fork