Create `DataTypeFeature` abstraction (for JSTEP-7) with placeholder features

So, this is the initial issue for work towards

https://github.com/FasterXML/jackson-future-ideas/wiki/JSTEP-7

although does not actually implement support for actually using such features: this is just for initial scaffolding.
The idea is to create new issues and implement them for 2.14, however, immediately after getting this added.

