Support toString for AdaptedFunctionReference subclasses

Also make it serializable like other lambdas, suspend lambdas and normal
callable references.

libraries/stdlib/jvm/runtime/kotlin/jvm/internal/AdaptedFunctionReference.java

@@ -8,6 +8,8 @@ package kotlin.jvm.internal;
 import kotlin.SinceKotlin;
 import kotlin.reflect.KDeclarationContainer;
 
+import java.io.Serializable;
+
 import static kotlin.jvm.internal.CallableReference.NO_RECEIVER;
 
 /**
@@ -24,7 +26,7 @@ import static kotlin.jvm.internal.CallableReference.NO_RECEIVER;
  */
 @SuppressWarnings({"rawtypes", "WeakerAccess", "unused"})
 @SinceKotlin(version = "1.4")
-public class AdaptedFunctionReference {
+public class AdaptedFunctionReference implements FunctionBase, Serializable {
     protected final Object receiver;
     private final Class owner;
     private final String name;
@@ -47,6 +49,11 @@ public class AdaptedFunctionReference {
         this.flags = flags >> 1;
     }
 
+    @Override
+    public int getArity() {
+        return arity;
+    }
+
     public KDeclarationContainer getOwner() {
         return owner == null ? null :
                isTopLevel ? Reflection.getOrCreateKotlinPackage(owner) : Reflection.getOrCreateKotlinClass(owner);
@@ -77,4 +84,9 @@ public class AdaptedFunctionReference {
         result = result * 31 + flags;
         return result;
     }
+
+    @Override
+    public String toString() {
+        return Reflection.renderLambdaToString(this);
+    }
 }