Adds interoperability between UIKit and SwiftUI to SwiftCurrent

[Tyler-Keith-Thompson]

Linked Issue:

Checklist:

• [x] Did you sign the Contributor License Agreement?
• [x] Is the linter reporting 0 errors?
• [x] Did you comply with our styleguide?
• [x] Is there adequate test coverage for your new code?
• [x] Does the CI pipeline pass?
• [x] Did you update the documentation?
• [x] Did you update the sample app?
• [x] Do we need to increment the minor/major version?
• [x] Did you change the public API?
• [x] Have you done everything you can to make sure that errors that can occur are compile-time errors, and if they have to be runtime do you have adequate tests and documentation around those runtime errors? For more details.

[codecov-commenter]

Codecov Report

Merging #97 (a73bbba) into main (8bf1e5b) will increase coverage by 0.07%. The diff coverage is 96.77%.

@@            Coverage Diff             @@
##             main      #97      +/-   ##
==========================================
+ Coverage   94.71%   94.79%   +0.07%     
==========================================
  Files          62       65       +3     
  Lines        1608     1670      +62     
==========================================
+ Hits         1523     1583      +60     
- Misses         85       87       +2     

Impacted Files	Coverage Δ
...rent_SwiftUI/UIKitInterop/HostedWorkflowItem.swift	90.00% <90.00%> (ø)
...terop/UIKitInteropProgrammaticViewController.swift	97.14% <97.14%> (ø)
...tCurrent_SwiftUI/Views/ViewControllerWrapper.swift	100.00% <100.00%> (ø)
Sources/SwiftCurrent_SwiftUI/WorkflowItem.swift	100.00% <100.00%> (ø)

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[Tyler-Keith-Thompson]

https://user-images.githubusercontent.com/33705774/128616934-b8ed9c4a-6cee-4add-902f-073cade71a64.mp4

Here's a video of the PR in action. The first view is the UIViewController from our programmatic getting started guide. The second screen is a SwiftUI view. They're described as part of the same Workflow and it just works.

The sample app wasn't modified this way for everybody, just for the video demo.