root: introduce down-propagating Helper.BlockState for other directives/plugins to use (#7594)

* add 'root' key to Helper.State for access in frankenphp's `php_server` directive

* clone state before passing it to child directives, but keep sharing it among sibling directives

* propagate named route state from children to parent

* use BlockState to set "root" instead

* gofmt -w .

* go fmt ./...

* here we go