Mark managed atomic constructs Sendable if their payloads are

[lorentey]

Resolves #45.

Checklist

• [X] I've read the Contribution Guidelines
• [X] My contributions are licensed under the Swift license.
• [X] I've followed the coding style of the rest of the project.
• [ ] I've added tests covering all new code paths my change adds to the project (if appropriate).
• [X] I've verified that my change does not break any existing tests.
• [ ] I've updated the documentation if necessary.

[lorentey]

@swift-ci test

[lorentey]

17:36:08 
/Users/buildnode/jenkins/workspace/pr-swift-atomics-macos/branch-main/swift-atomics/Sources/Atomics/autogenerated/HighLevelTypes.swift:105:26: error: unknown attribute 'unchecked'
17:36:08 extension ManagedAtomic: @unchecked Sendable where Value: Sendable {}
17:36:08                          ^
17:36:08 /Users/buildnode/jenkins/workspace/pr-swift-atomics-macos/branch-main/swift-atomics/Sources/Atomics/autogenerated/HighLevelTypes.swift:82:14: error: non-final class 'ManagedAtomic' cannot conform to `Sendable`; use `UnsafeSendable`
17:36:08 public class ManagedAtomic<Value: AtomicValue> {
17:36:08              ^

ಠ_ಠ

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test macOS platform

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test

[lorentey]

@swift-ci test

[jpsim]

It'd be great to land this so consumers don't need to @preconcurrency import Atomics.

[weissi]

It'd be great to land this so consumers don't need to @preconcurrency import Atomics.

+1

[lorentey]

@swift-ci test