RevEng: Strive for reusing common annotations and metadata APIs

[divega]

Our reverse engineering pipeline uses an IModel that is not bound to CLR types as a representation at various stages, including the model that is passed to the final code generation stage.

Note that IModels that are not bound to CLR types aren't full fidelity with all the capabilities of EF, e.g. per see #2140 it is not possible to represent unbound navigation properties. However, we should strive to reuse all the capabilities that are first class when we can, e.g. favor general purpose well-known annotations vs. reverse engineering-specific annotations for things like table names and column names, column types, and produce/consume the annotation through the strongly typed APIs we have created for that purpose, etc.

[rowanmiller]

@lajones is this done now?

[lajones]

There's one more small place where I want to update the code.

[lajones]

This is now done with commit 057b8df.