This commit updates Meta/import-webkit-regexp-tests.py and re-imports
WebKit tests.
Removed pcre-test-1 from SKIP_TESTS because we pass it.
Removed everything except slow.js from XFAIL_TESTS. We pass everything
except slow.js, which still hits the step limit.
Moved overflow.js to SKIP_FILES because it tests WebKit's behaviour of
rejecting regexps with huge quantifiers. Ladybird, Chrome, and Firefox
just clamp them.
Add scripts for importing the V8 and WebKit regexp suites into
`Tests/LibJS/Runtime/3rdparty/` and commit the imported tests.
Also update the local harness helpers so these suites can run under
LibJS. In particular, teach the assertion shims to compare RegExp values
the way the imported tests expect and to treat `new Function(...)`
throwing as a valid `assertThrows` case.
This gives the regex rewrite a large bank of external conformance tests
that exercise parser and matcher behavior beyond in-tree coverage.
