CoreUtil::checkAccess() - Accept optional argument $userID

CoreUtil::checkAccess() - Accept optional argument $userID

Technically, there is an inheritable contract-change here - modifying
`isAuthorized()` to accept the current user ID. However, I grepped
universe for references:

```
[bknix-min:~/bknix/build/universe] grep -ri isAuthorized $( find -name Civi )
```

And all references were internal to `civicrm-core.git`.  This makes some
sense, given the available alternative extension-points
(`Civi\Api4\$ENTITY::permissions()` and `civi.api.authorize`).