Investigate which FFI types are still in the tss-esapi interface

[ionut-arm]

Now that we have a separation between the tss-esapi and tss-esapi-sys crates, we should focus on removing all FFI data types from the interface of tss-esapi. While we cannot change the interface for any 5.x.y release, we can still write up abstractions for all these types and replace them when we're ready for a major version bump.

This issue is just an investigation for which types are still being used straight from -sys. New interfaces SHOULD NOT use FFI types and should instead create new abstractions (or use the Rust native types, if they exist).

Depending on how difficult to abstract they are, we could create separate issues for the work, e.g. a separate issue for TPM2B_PUBLIC.

[Superhepper]

This is now part of the much larger issue #290 can there for be closed.