Consider enabling more features on the C FFI crate

[tmathern]

The C FFI has currently two features enabled from the core SDK: file_io and rust_native_crypto as seen here.

It seems though that we need more features enabled, eg. pdf (here). I believe enabling PDF would solve the issue reported on Python side here: contentauth/c2pa-python#131, as the C FFI crate defines the C interface and directs what is available in the native libraries the Python bindings are built upon.

@gpeacock @mauricefisher64 Do you think there are other features that should be enabled for the C FFI? How strong of a gatekeeping do we want/need to decide to enable those?

[gpeacock]

This looks like the only one we need to add right now, but yes, we should add PDF read support.

[gpeacock]

FYI It also now includes fetch_remote_manifests and add_thumbnails

[tmathern]

PR with change is merged!