url: make the context non-enumerable

At the moment we expose the context as a normal property on the
prototype chain of URL or take them from the base URL
which makes them enumerable and considered
by assert libraries even though the context carries path-dependent
information that do not affect the equivalence of these objects.
This patch fixes it in a minimal manner by marking the context
non-enumerable as making it full private would require more
refactoring and can be done in a bigger patch later.

PR-URL: https://github.com/nodejs/node/pull/24218
Refs: https://github.com/nodejs/node/issues/24211


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>