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.
