Support referencing and re-exporting types from other libs for type sharing

[leighmcculloch]

What problem does your feature solve?

It's desirable to be able to export types from a contract that have been defined in another crate or contract.

See discussions about doing that here:

• https://discord.com/channels/897514728459468821/1281696488199553025

What would you like to see?

Ideally a way to use a type in a contract functions interface, where that type is defined in another crate or another contract.

What alternatives are there?

A manual way to redefine the same type, as a type-alias of sorts, and somehow adopt the structure of the type defined elsewhere and be compatible.

[leighmcculloch]

This issue is similar and related to:

• Explore ways to support contract extensibility #1326