This modification should not change anything logically.

Introduce a couple of methods (without using it) to identify
internal links, in terms of:

• anchors
• relative URLS
• absolute URLs that do not point to the internal base URI

https://we.phorge.it/T15182

Identifying these case could be useful to decide to apply
further logics in the future, out of the scope of this patch.

Closes T15182

• Verify that nothing has changed logically