Re-introduce the `selector-native` similar to the one on the `3.x-stable`
branch. One difference is since the `main` branch inlined Sizzle, some
selector utils can be shared between the main `selector` module and
`selector-native`.
The main `selector` module can be disabled in favor of `selector-native`
via:
grunt custom:-selector
Other changes:
* Tests: Fix Safari detection - Chrome Headless has a different user
agent than Safari and a browser check in selector tests didn't take
that into account.
* Tests: Run selector-native tests in `npm test`
* Selector: Fix querying on document fragments
Ref gh-4395
Closes gh-5085
4c1171f2ed