Implement Throwable.unwrap accordingly to the target platform. Fix #1404

mirai-core-utils/src/androidMain/kotlin/Actuals.kt

@@ -21,4 +21,16 @@ public actual fun ByteArray.encodeBase64(): String {
 
 public actual fun String.decodeBase64(): ByteArray {
     return Base64.decode(this, Base64.DEFAULT)
-}
+}
+
+public actual inline fun <reified E> Throwable.unwrap(): Throwable {
+    if (this !is E) return this
+    if (suppressed.isNotEmpty()) return this
+    val e =
+        Exception("unwrapped exception: $this").also {  // Android JDK could not resolve circular references so we copy one.
+            it.stackTrace = this.stackTrace
+        }
+    return this.findCause { it !is E }
+        ?.also { it.addSuppressed(e) }
+        ?: this
+}

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

@@ -157,13 +157,7 @@ public fun Throwable.unwrapCancellationException(): Throwable = unwrap<Cancellat
  *     at net.mamoe.mirai.internal.network.impl.netty.NettyNetworkHandler.close(NettyNetworkHandler.kt:404)
  * ```
  */
-
-public inline fun <reified E> Throwable.unwrap(): Throwable {
-    if (this !is E) return this
-    if (suppressed.isNotEmpty()) return this
-    return this.findCause { it !is E }
-        ?.also { it.addSuppressed(this) }
-        ?: this
-}
+@Suppress("unused")
+public expect inline fun <reified E> Throwable.unwrap(): Throwable
 
 public val CoroutineContext.coroutineName: String get() = this[CoroutineName]?.name ?: "unnamed"

mirai-core-utils/src/jvmMain/kotlin/Actuals.kt

@@ -21,4 +21,12 @@ public actual fun ByteArray.encodeBase64(): String {
 
 public actual fun String.decodeBase64(): ByteArray {
     return Base64.getDecoder().decode(this)
-}
+}
+
+public actual inline fun <reified E> Throwable.unwrap(): Throwable {
+    if (this !is E) return this
+    if (suppressed.isNotEmpty()) return this
+    return this.findCause { it !is E }
+        ?.also { it.addSuppressed(this) }
+        ?: this
+}