Add Support for Threadsafe and NotThreadSafe annotations

Samples/JavaKitSampleApp/Sources/JavaKitExample/JavaKitExample.swift

@@ -76,6 +76,9 @@ extension HelloSwift: HelloSwiftNativeMethods {
       print("Caught Java error: \(error)")
     }
 
+    // Make sure that the thread safe class is sendable
+    let threadSafe: Sendable = ThreadSafeHelperClass(environment: javaEnvironment)
+
     return i * j
   }
 

Samples/JavaKitSampleApp/Sources/JavaKitExample/com/example/swift/ThreadSafe.java

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ThreadSafe {
+}

Samples/JavaKitSampleApp/Sources/JavaKitExample/com/example/swift/ThreadSafeHelperClass.java

@@ -0,0 +1,6 @@
+package com.example.swift;
+
+@ThreadSafe
+public class ThreadSafeHelperClass {
+    public ThreadSafeHelperClass() { }
+}

Samples/JavaKitSampleApp/Sources/JavaKitExample/swift-java.config

@@ -2,6 +2,7 @@
   "classes" : {
     "com.example.swift.HelloSwift" : "HelloSwift",
     "com.example.swift.HelloSubclass" : "HelloSubclass",
-    "com.example.swift.JavaKitSampleMain" : "JavaKitSampleMain"
+    "com.example.swift.JavaKitSampleMain" : "JavaKitSampleMain",
+    "com.example.swift.ThreadSafeHelperClass" : "ThreadSafeHelperClass"
   }
 }