Refactor FXIOS-14485 [Swift 6 Migration] Re-enable Swift 6 on the Client at the project level

[ih-codes]

📜 Tickets

Jira ticket
Github issue

💡 Description

Because of some issues with the stricter Swift 6 compiler stripping code out of our release builds, we decided to revert our migration to Swift 6 in #31793.

Original migration happened in #31483.

We are now testing re-enabling the migration as we have a pipeline_build_and_test_release pipeline from the Test Engineering team to run our UI tests against release builds. So I will trigger that to validate that the Swift 6 migration hasn't caused further undetected issues in release builds specifically.

📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code

[mobiletest-ci-bot]

	Warnings
⚠️	Detected shell script changes in: test-fixtures/generate-metrics.sh (cc @adudenamedruby)

	Messages
📖	Project coverage: 40.28%

💪 Quality guardian

1 tests files modified. You're a champion of test coverage! 🚀

🧹 Tidy commit

Just 4 file(s) touched. Thanks for keeping it clean and review-friendly!

💬 Description craftsman

Great PR description! Reviewers salute you 🫡

✅ New file code coverage

No new file detected so code coverage gate wasn't ran.

Client.app: Coverage: 38.38

File	Coverage
NativeErrorPageMiddleware.swift	0.0%	⚠️

Generated by 🚫 Danger Swift against 7e6b8cf

[lmarceau]

Can we lower the warnings count again with this re-enablement?

[ih-codes]

Can we lower the warnings count again with this re-enablement?

You're a ninja, I opened a draft so no one would get bothered by this yet! 😆

Yep I'm doing that right now and fixing some warnings. I think I can get it lower than the current 7 warnings because some other warnings got introduced recently that aren't even Swift 6 related.

[ih-codes]

There was a warning because nothing in windowManager.tabManager(for: windowUUID).selectedTab actually throws, so I removed the whole try block.