re-export crates from capnp

[andrewbanchich]

hi @dwrensha! we currently use capnp, capnpc, and capnp-rpc. when dependabot updates our dependencies, it opens one PR per update, which causes problems with capnp since sometimes this breaks CI due to these depending on each other.

e.g. with the 0.24 update the PR for updating capnpc fails with:

error[E0599]: no function or associated item named `new` found for struct `capnp::introspect::RawStructSchema` in the current scope

would it be possible to re-export capnpc and capnp-rpc from capnp (maybe behind a feature flag if you want to optimize build times) so that these always stay in sync?