Fix deprecation warnings in iOS Swift Keychain Wrapper code

[lmarceau]

Hello! I've been seeing some warnings and deprecations while using A-S and would love to provide a fix for them. I've notice this code is based on the SwiftKeychainWrapper project, and a contributor over there fixed those warnings so this PR is based on those changes (although it's not a 1 to 1 since we have MZ prefixes on some classes).

First time contributing on this project, so not sure how to properly run this as this Swift project doesn't work the standard way I normally run things. Please let me know how I can improve this PR.

Pull Request checklist

• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGES_UNRELEASED.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due dilligence applied in selecting them.

Branch builds: add [ff-android: firefox-android-branch-name] and/or [fenix: fenix-branch-name] to the PR title.

[codecov-commenter]

Codecov Report

Base: 44.29% // Head: 44.30% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (a7c7c5d) compared to base (c4368db).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5259      +/-   ##
==========================================
+ Coverage   44.29%   44.30%   +0.01%     
==========================================
  Files         175      175              
  Lines       13899    13898       -1     
==========================================
+ Hits         6157     6158       +1     
+ Misses       7742     7740       -2     

Impacted Files	Coverage Δ
components/tabs/src/sync/engine.rs	0.00% <0.00%> (ø)
components/sync15/src/client/token.rs	0.00% <0.00%> (ø)
components/fxa-client/src/internal/oauth.rs	0.00% <0.00%> (ø)
components/fxa-client/src/internal/http_client.rs	0.00% <0.00%> (ø)
tools/protobuf-gen/src/main.rs	96.29% <0.00%> (+0.14%)	⬆️

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[tarikeshaq]

Thanks for the PR @lmarceau 🙏

The CI job for iOS is failing due to a few cannot be resolved without a contextual type

You can try opening the xcode project in application-services/megazords/ios-rust/MozillaTestServices

Then running build on Xcode should show the errors!

[tarikeshaq]

Thank @lmarceau 🚀 Since this is deprecation fix/refactor we don't need a changelog so I'm landing this!