Add runtime annotation support to model

[AndriySvyryd]

1. These annotations provide caching capabilities to the model.
2. Can only be added after a model is built
3. Aren't returned with normal annotations

Can be used to store the relational model, TypeMappingSource, relational overrides (that don't affect configuration), property indexes/accessors, generating/propagating properties in ValueGenerationManager

Related to #9329, #19213, #19806 and #21901

Also review the nullability of some methods: GetKeyValueComparer, CreateDependentsMapFactory, etc...