Allow TypeMappingSource to use the pre-convention configuration

[AndriySvyryd]

Splitting this out from #10784 (comment):

Ideally, TypeMappingSource would return the correct mapping for a given type after this change. However, the correct mapping will now depend on the model, or at least some part of the model. This is problematic because TypeMappingSource is a singleton service and is used extensively by other singleton services. Changing these all to scoped is not feasible. Two ways I can think of that might work are:

• Passing in the model whenever we ask for a type mapping from the source. This requires non-trivial flow of the model to places it isn't now.
• Have the source return some kind of deferred mapping, which is only later resolved to the real mapping when the model is available. I've been experimenting with this and it seems promising, but it is again not a trivial change.

[AndriySvyryd]

We'll also need to

• Add IMappingConfiguration? FindMappingConfiguration(Type type) method to IModel
• Implement IMappingConfiguration in PropertyConfiguration
• Add runtime implementation RuntimeMappingConfiguration
• Add compiled model generation support