Performance improvements.
$dynamicRef/$dynamicAnchor support (from draft-2020-12).
Initial draft-2020-12 support, without the "contains" keyword.

"contains" keyword in draft-2020-12 throws for now on compile, to ensure
that the contains/unevaluatedItems combo won't be processed incorrectly,
as that behavior changed in draft-2020-12 and that is not yet supported.