Document lists research: Downcast via reconversion

[Mgsy]

No description provided.

[niegowski]

While preparing a PoC we realized that we don't have an API that would allow us to generate some view structure from some model element attributes and then place the element itself inside that structure. This makes the low-level conversion really complicated (even without handling all use-cases) so we decided that we need to implement sort of "slot-able" conversion as described in #9783 and then we shall use it for document lists (#9784)