ci: move iOS13-Swift under xcodegen mgmt

[armcknight]

following #5116, moving app projects to xcodegen. this is the last app that was under iOS-Swift.xcodeproj, so that xcodeproj file is now able to be removed here.

Also, renamed the directory containing the ui test sources from iOS13-SwiftTests to iOS13-Swift-UITests for consistency and clarity.

#skip-changelog; for #5165

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.785%. Comparing base (2661001) to head (58a5894).

Additional details and impacted files

@@                           Coverage Diff                           @@
##           armcknight/ci/ios-swift6-xcodegen     #5117       +/-   ##
=======================================================================
+ Coverage                             92.756%   92.785%   +0.029%     
=======================================================================
  Files                                    669       677        +8     
  Lines                                  83800     84414      +614     
  Branches                               30405     30694      +289     
=======================================================================
+ Hits                                   77730     78324      +594     
- Misses                                  5973      5988       +15     
- Partials                                  97       102        +5     

see 63 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2661001...58a5894. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1217.40 ms	1241.53 ms	24.14 ms
Size	22.31 KiB	852.06 KiB	829.75 KiB

Baseline results on branch: armcknight/ci/ios-swift6-xcodegen

Startup times

Revision	Plain	With Sentry	Diff
38fdac7	1227.86 ms	1255.69 ms	27.84 ms

App size

Revision	Plain	With Sentry	Diff
38fdac7	22.30 KiB	852.05 KiB	829.75 KiB

Previous results on branch: armcknight/ci/ios13-swift-xcodegen

Startup times

Revision	Plain	With Sentry	Diff
a8bb710	1229.10 ms	1247.94 ms	18.83 ms

App size

Revision	Plain	With Sentry	Diff
a8bb710	22.31 KiB	852.05 KiB	829.74 KiB