Support lexicographical data (lexemes)

[mormegil-cz]

WikiClientLibrary currently misses BuiltInDataTypes for Wikidata’s lexicographical data.

As far as I can tell, basically three new definitions of the data types, plus a more general implementation of EntityIdFromJson+EntityIdToJson is needed.

See my quick-and-dirty implementation of those (also including a copy-paste of the inaccessible internal sealed DelegatePropertyType from the library) which seems to work fine.

[CXuesong]

Thanks for pointing this out! Regretfully I may not have enough time at the moment 🌚 I'll look into this when I'm available (might be much later).

Just in case you have some time available during the next few months, probably you can propose a PR so that you can at least have something from WCL library without any hacking.

[CXuesong]

Okay I've checked the documentation and realized this is a concept like Item / Property / Entity. Then I guess we'd better wait for a while until I have some more time to look into it.