(Maint)|Export Dynamic library for SwiftPM

[eneko]

• I've read, understood, and done my best to follow the CONTRIBUTING guidelines.

This pull request includes (pick all that apply):

• Bugfixes
• New features
• Breaking changes
• Documentation updates
• Unit tests
• Other

Summary

Applications with extensions (eg. Today Widget) that consume Conduit via SwiftPM will need to import Conduit as a dynamic framework starting in Xcode 11.4.

Implementation

• Package definition has been updated to export both static and dynamic libraries
  • A new dynamic library has been added as ConduitDynamic

Test Plan

• Run all tests

[codecov]

Codecov Report

Merging #148 into master will decrease coverage by 0.59%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
- Coverage   79.67%   79.08%   -0.60%     
==========================================
  Files          70       70              
  Lines        2755     2529     -226     
==========================================
- Hits         2195     2000     -195     
+ Misses        560      529      -31     

Flag	Coverage Δ
#main	79.08% <ø> (-0.60%)	⬇️

Impacted Files	Coverage Δ
Sources/Conduit/Auth/Vendor/KeychainWrapper.swift	39.77% <0.00%> (-3.63%)	⬇️
...es/Conduit/Networking/Images/ImageDownloader.swift	85.10% <0.00%> (-3.03%)	⬇️
...etworking/Serialization/ResponseDeserializer.swift	91.66% <0.00%> (-2.09%)	⬇️
...g/Serialization/FormEncodedRequestSerializer.swift	92.30% <0.00%> (-1.81%)	⬇️
...it/Auth/TokenGrants/OAuth2TokenGrantStrategy.swift	90.00% <0.00%> (-1.67%)	⬇️
...tworking/Serialization/JSONRequestSerializer.swift	90.32% <0.00%> (-1.57%)	⬇️
...e/Coordination/OAuth2TokenRefreshCoordinator.swift	86.66% <0.00%> (-1.57%)	⬇️
...Serialization/MultipartFormRequestSerializer.swift	86.61% <0.00%> (-1.42%)	⬇️
Sources/Conduit/Auth/OAuth2TokenGrantManager.swift	80.48% <0.00%> (-1.34%)	⬇️
Sources/Conduit/Networking/SessionTaskProxy.swift	76.47% <0.00%> (-1.31%)	⬇️
... and 27 more

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[johnhammerlund]

This will change the current target from static to dynamic, correct? Would it be safer to instead create a ConduitDynamic target?

[eneko]

It seemed to me that for most of our apps we were going to need the dynamic one, so I made that one the "default". But yes, we can do it that way. It would prevent any impact on anyone currently using Conduit via SwiftPM without this issue.

Will switch them now.