Kotlinify SingleThreadAsserter (#43768)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/43768

Changelog: [Internal]

As part of the Sustainability Week (see [post](https://fb.workplace.com/groups/251759413609061/permalink/742797531171911/)).

Reviewed By: cortinico

Differential Revision: D55636773

fbshipit-source-id: 2f3d1c73a5d3c7d229b854ab73dcf2902a639c3a

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -1746,9 +1746,9 @@ public abstract interface class com/facebook/react/common/ShakeDetector$ShakeLis
 	public abstract fun onShake ()V
 }
 
-public class com/facebook/react/common/SingleThreadAsserter {
+public final class com/facebook/react/common/SingleThreadAsserter {
 	public fun <init> ()V
-	public fun assertNow ()V
+	public final fun assertNow ()V
 }
 
 public final class com/facebook/react/common/StandardCharsets {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/common/SingleThreadAsserter.java

@@ -1,26 +0,0 @@
-/*
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-package com.facebook.react.common;
-
-import androidx.annotation.Nullable;
-import com.facebook.infer.annotation.Assertions;
-import com.facebook.infer.annotation.Nullsafe;
-
-/** Simple class for asserting that operations only run on a single thread. */
-@Nullsafe(Nullsafe.Mode.LOCAL)
-public class SingleThreadAsserter {
-  private @Nullable Thread mThread = null;
-
-  public void assertNow() {
-    Thread current = Thread.currentThread();
-    if (mThread == null) {
-      mThread = current;
-    }
-    Assertions.assertCondition(mThread == current);
-  }
-}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/common/SingleThreadAsserter.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.common
+
+import com.facebook.infer.annotation.Assertions
+
+/** Simple class for asserting that operations only run on a single thread. */
+public class SingleThreadAsserter {
+  private var thread: Thread? = null
+
+  public fun assertNow() {
+    val currentThread = Thread.currentThread()
+    if (thread == null) {
+      thread = currentThread
+    }
+    Assertions.assertCondition(thread == currentThread)
+  }
+}