Fix SPM compilation

[vmanot]

Fixes #82, building upon #26.

You would not believe the number of hacks I went through to get this to work.

Implementation

• Create a new module ProtonCore - to be consumed by Proton (still a single package though)
• Move Objective-C files to ProtonCore
• Add interfaces to the the ObjC files to allow it to work with with Proton's ObjC declarations.
• Modify Proton to cast wherever appropriate.

[rajdeep]

@vmanot, it seems that the files have not been correctly referenced in the Project. The build is failing for the same reason: https://github.com/rajdeep/proton/pull/82/checks

This is what I see on local machine:

[YoX89]

I see the same as @rajdeep. I tried to manually fix the reference issues but it wasn't enough it seems. Importing this branch as a Swift Package works but building it locally doesn't.

The reason is that the local project needs to have the ProtonCore framework as well. Otherwise the import ProtonCore statements won't compile, which makes sense because ProtonCore only exists in SPM. So I think the solution is to first fix the references and then create a ProtonCore framework that mirrors the SPM ProtonCore target.

[rajdeep]

Superseded by #110. Thanks for your efforts and input, @vmanot

[rajdeep]

@YoX89 the changes were beyond just fixing the references as over time there was cyclic dependency created between ObjC and Swift code. Since ObjC code now needed it's own module, I had to change bits to break the dependency of ObjC code on Swift. You should be able to try the latest branch for spm-support with SPM.