Migrate to DirectedCodegen

[aajtodd]

Consider what it would take to migrate to some of the newer utilities like DirectedCodegen

The background here is that the Smithy team took a lot of the best patterns found in Kotlin/Rust/Go/etc and internalized them. We don't have to migrate but long term it may be better to standardize on what Smithy is supporting rather than owning all of the utils we have built up. I'm not sure where the API differences are though or how difficult a migration this may be.

We should also consider any other custom utilities that now have found an official equivalent in Smithy.