[Improvements] The projection tooling improvements

[kotlarmilos]

Description

This issue comprises ideas and features for tooling improvements based on feedback. The more ideas will be added as we collect feedback.

• User type specification: Allow users to specify binding and non-binding types.
• API aggregation: Aggregate public APIs without requiring a .swift source library, relying solely on the .swiftmodule file.

[rolfbjarne]

• API aggregation: Aggregate public APIs without requiring a .swift source library, relying solely on the .swiftmodule file.

I believe we shouldn't need more than what Swift itself needs? So if you want to use a Swift library from Swift code, and the Swift compiler only needs the .swiftmodule, then we should be able to figure things out with just the .swiftmodule.