Source-generated EDM metadata and dictionary-based serialization

[kzu]

Right now we have a reflection-based EntityPropertiesMapper, that only supports primitive types (or fails at run-time).

We could use a compile-time source generator (no need to actually emit anything for intellisense, since this is all for run-time) that implements an interface (i.e. IEntitySerializable) so that the mapper can check if the entity to convert supports this mechanism and avoid any reflection altogether.

This could also be the foundation for arbitrary object graphs to be persisted in primitive columns too, in particular for complex-type record properties that improve API design like structured Address and the like. So perhaps not lists and collections, but nested properties only?