[pigeon] [swift] Changes PigeonError class to conform to Sendable.

[bc-lee]

Make PigeonError conform to Sendable for compatibility with Swift 6.0 mode by changing the details property type from Any? to Sendable?.

Fixes flutter/flutter#160313

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[hellohuanlin]

This will break old sdk where Sendable is undefined. You may have to put it behind a flag.

[bc-lee]

This will break old sdk where Sendable is undefined. You may have to put it behind a flag.

Are there any minimum Xcode requirements for Flutter projects? Sendable was added in Xcode 13.0 with Swift 5.5.

[bc-lee]

I found the answer.

• Flutter 3.12 or later requires Xcode 14.0 or newer.
  Source
• Flutter 3.0 or later requires Xcode 13.0 or newer.
  Source

So, I think it is safe to use this in Pigeon, as Pigeon requires Dart 3.3 and Flutter 3.19.

[tarrinneal]

This should be updated to 22.7.1 along with the pubspec version and the generator_tools file.

I guess this is technically a breaking change, so 23.0.0 might be more correct.

[tarrinneal]

[swift] Changes `PigeonError` class to conform to `Sendable`.

[tarrinneal]

@stuartmorgan shouldn't this pr be failing the test exemption check?

[hellohuanlin]

lgtm after addressing the comments.

[stuartmorgan]

@stuartmorgan shouldn't this pr be failing the test exemption check?

I think there's a false negative due to the changes to generated files in platform_tests; we should probably tune the Cocoon rules to ignore .gen. files in there.

Regardless, this does need testing. A Dart unit test should be fine for this for now (although long term we probably want to adjust the Swift integration tests to actually test a flow that ensures that everything is Sendable)