Use `GenericTypes`'s type resolver instead of re-resolving

When we resolve a type with `GenericTypes::maybe_resolve_path` it
returns a resolved-path string as well as a syn::Path. When
resolving we'd previously then re-resolve the Path with the current
type/import information, instead of just accepting what was already
resolved. Simply accepting what was already resolved not only
simplifies a few cases, but also allows us to clean up where the
"crate::" prefix is printed, keeping "crate::" prefixes out of all
type resolution.