`weak` property in `Sendable` type leaks implementation detail

[NachoSoto]

Describe the bug Using weak on a Sendable class leads to a bad diagnostic.

Steps To Reproduce

final class A: NSObject, Sendable {
    lazy var a: String = "test"
}

Expected behavior

Stored property 'a' of 'Sendable'-conforming class 'A' is mutable

Actual behavior

Stored property '$__lazystorage$_a' of 'Sendable'-conforming class 'A' is mutable

Environment (please fill out the following information)

• OS: macOS 13.0
• Xcode: 14.0 beta 4
• Swift: 5.7 (swiftlang-5.7.0.123.7 clang-1400.0.29.50)

[CodaFi]

Tracked internally as rdar://86926732

[NachoSoto]

This is still happening on Swift 6.