[SwiftData] Classes qualified with @model macro allow incomplete initializers

FB12645485

Classes qualified with @Model macro allow incomplete initializers

The compiler does not throw an error if a class with @Model, as in the following code, implements only an incomplete initializer (in this example, the properties are not initialized at all).
This would normally (if the plain class is not macro qualified) result in a compile error "Return from initializer without initializing all stored properties".

```swift
import SwiftData

@Model
final class Event {
  var title: String
  var start: Date
  var end: Date

  init(title: String, start: Date, end: Date) {
    // This initializer does not initialize any properties
  }
}
```

Properties that should be initialized are not, so the class will crash with a runtime error if any of the properties are accessed.

This behaviour in SwiftData breaks type safety.

This example is extreme, but consider another case where a property is added to an existing class, like the following:

```swift
@Model
final class Event2 {
  var title: String
  var start: Date
  var end: Date

  var isDeleted: Bool // Added this propety.

  init(title: String, start: Date, end: Date) {
    self.title = title
    self.start = start
    self.end = end
    // Forgot to add initialize the property
  }
}
```

If you then forget to add initialization for that property to the initializer, you have an error that is hard to notice and debug.
Classes qualified with @Model macros should have no different compile time behaviour than plain classes.

Fix on iOS 17.1.