fix: Avoid RegExp lookbehind assertions (#3816) (#3817)

* fix: Avoid RegExp lookbehind assertions (#3816)

RegExp lookbehind assertions are supported in Safari >= 16.5, avoiding them
keeps support for older Safari versions.

* Improve perf of blockSkip on modern engines

RegExp lookbehind assertions are supported in Safari >= 16.5. But the
lookbehind-less version has a performance penalty. So having a fallback keeps
support for older Safari versions while maintaining performance for modern
engines.

* Add comment about lookbehind browser support

As suggested by @styfle

Co-authored-by: Steven <steven@ceriously.com>

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Co-authored-by: Steven <steven@ceriously.com>