Add utils threadLocal

mirai-core-utils/src/commonMain/kotlin/ThreadLocal.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2019-2021 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
+ */
+
+package net.mamoe.mirai.utils
+
+import kotlin.reflect.KProperty
+
+
+public fun <T : Any?> threadLocal(newInstance: () -> T): ThreadLocal<T> {
+    return object : ThreadLocal<T>() {
+        override fun initialValue(): T = newInstance()
+    }
+}
+
+public operator fun <T> ThreadLocal<T>.getValue(t: Any?, property: KProperty<Any?>): T = this.get()