Improve toString() for lambdas and function expressions

#KT-9952 Fixed

core/runtime.jvm/src/kotlin/jvm/internal/Lambda.kt

@@ -19,6 +19,5 @@ package kotlin.jvm.internal
 abstract class Lambda(private val arity: Int) : FunctionImpl() {
     override fun getArity() = arity
 
-    @Suppress("PLATFORM_CLASS_MAPPED_TO_KOTLIN")
-    override fun toString() = "${(this as Object).`class`.genericInterfaces[0]}"
+    override fun toString() = Reflection.renderLambdaToString(this)
 }

core/runtime.jvm/src/kotlin/jvm/internal/Reflection.java

@@ -74,6 +74,10 @@ public class Reflection {
         return kClasses;
     }
 
+    public static String renderLambdaToString(Lambda lambda) {
+        return factory.renderLambdaToString(lambda);
+    }
+
     // Functions
 
     public static KFunction function(FunctionReference f) {

core/runtime.jvm/src/kotlin/jvm/internal/ReflectionFactory.java

@@ -19,6 +19,8 @@ package kotlin.jvm.internal;
 import kotlin.reflect.*;
 
 public class ReflectionFactory {
+    private static final String KOTLIN_JVM_FUNCTIONS = "kotlin.jvm.functions.";
+
     public KClass createKotlinClass(Class javaClass) {
         return new ClassReference(javaClass);
     }
@@ -39,6 +41,11 @@ public class ReflectionFactory {
         return new ClassReference(javaClass);
     }
 
+    public String renderLambdaToString(Lambda lambda) {
+        String result = lambda.getClass().getGenericInterfaces()[0].toString();
+        return result.startsWith(KOTLIN_JVM_FUNCTIONS) ? result.substring(KOTLIN_JVM_FUNCTIONS.length()) : result;
+    }
+
     // Functions
 
     public KFunction function(FunctionReference f) {