Add extension point for custom node type in document tree macro

Hello,

Thanks Marius for the proposal. The 3 solution are ok for me. In term of security I'm not sure that 1 is easy to make it secure (I think we might be falling back to the previous security ticket) even if it's the simplest solution and the most flexible. For 2 why not, it's fixing the issue, but I think if 3 is implemented it's enough we don't need 2 on LTS + 3 on master. And yes 3 look like the best solution.

Thanks.