Cosmos: Advanced type mapping inference (for scalar collections)

In various places in the Cosmos scalar collection implementation, we currently simply infer an array's type mapping from its CLR type; this loses type mapping information that may be configured on the array's element. Since Cosmos uses very little type mapping information, this mainly means that arrays over elements with value converters don't function correctly.

We should port over RelationalTypeMappingPostprocessor, which is a post-processing step for advanced type mapping inference from elements back to the arrays the came from.