FirestoreSwift: Reword DocumentID breaking change in changelog (#10305)

Updated the FirestoreSwift CHANGELOG to match the current state of the repo. Most users will be unaffected since the `@DocumentID` property wrapper constructors remain public but the changelog now warns that the `init(from documentReference: DocumentReference?)` constructor for `DocumentID` is internal.

In greater detail, the following is no longer possible:
```
let userDoc: DocumentReference = Firestore.firestore().document("users/foo")
do {
  let docID = try DocumentID<DocumentReference>(from: userDoc)
  if let docRef = docID.wrappedValue {
    print("Document ID: \(docRef.documentID)")
  }
} catch {
  print("DocumentID Error: \(error)")
}
```

The visibility change doesn't affect usage of `@DocumentID` though. The following is still possible (though it will trigger our warnings at runtime):
```
struct User: Codable {
  @documentid var docRef: DocumentReference? = Firestore.firestore().document("users/foo")
}
```

Author: andrewheard

Firestore/Swift/CHANGELOG.md

@@ -1,9 +1,10 @@
 # 10.0.0
-- [changed] **Breaking Change:** Made the `@DocumentID` property wrapper value
-  setter internal to clarify that the value is ignored during writes. (#9368)
-- [changed] Initializing a `@DocumentID` property wrapper with a non-nil value
-  or using the `@DocumentID` property wrapper value setter will log a warning.
-  This is because the set value will be ignored. (#9368)
+- [changed] **Breaking Change:** The `DocumentID` constructor from a
+  `DocumentReference` is now internal; this does not affect instantiating a
+  `@DocumentID` property wrapper for a `DocumentReference`. (#9368)
+- [changed] Passing a non-nil value to the `@DocumentID` property wrapper's
+  constructor or setter will log a warning and the set value will be ignored.
+  (#9368)
 - [changed] `Firestore.Encoder` and `Firestore.Decoder` now wraps the shared
   `FirebaseDataEncoder` and `FirebaseDataDecoder` types, which provides new
   customization options for encoding and decoding data to and from Firestore