Make anonymous classes for callable references synthetic

#KT-28453 Fixed

compiler/testData/codegen/box/callableReference/classesAreSynthetic.kt

@@ -0,0 +1,20 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND: JVM_IR
+// WITH_RUNTIME
+
+class C {
+    fun f() {}
+    val r = 0
+}
+
+fun check(c: Class<*>) {
+    if (!c.isSynthetic) throw AssertionError("Fail: $c is not synthetic: ${c.modifiers}")
+}
+
+fun box(): String {
+    check(C::f.javaClass)
+    check(C::r.javaClass)
+    check(C()::f.javaClass)
+    check(C()::r.javaClass)
+    return "OK"
+}

compiler/testData/codegen/bytecodeListing/noReceiverInCallableReferenceClasses.txt

@@ -7,7 +7,7 @@ public final class A {
 }
 
 @kotlin.Metadata
-final class NoReceiverInCallableReferenceClassesKt$A_bar$1 {
+synthetic final class NoReceiverInCallableReferenceClassesKt$A_bar$1 {
     public final static field INSTANCE: kotlin.reflect.KProperty1
     static method <clinit>(): void
     method <init>(): void
@@ -18,7 +18,7 @@ final class NoReceiverInCallableReferenceClassesKt$A_bar$1 {
 }
 
 @kotlin.Metadata
-final class NoReceiverInCallableReferenceClassesKt$A_foo$1 {
+synthetic final class NoReceiverInCallableReferenceClassesKt$A_foo$1 {
     public final static field INSTANCE: NoReceiverInCallableReferenceClassesKt$A_foo$1
     inner class NoReceiverInCallableReferenceClassesKt$A_foo$1
     static method <clinit>(): void
@@ -31,7 +31,7 @@ final class NoReceiverInCallableReferenceClassesKt$A_foo$1 {
 }
 
 @kotlin.Metadata
-final class NoReceiverInCallableReferenceClassesKt$aBar$1 {
+synthetic final class NoReceiverInCallableReferenceClassesKt$aBar$1 {
     method <init>(p0: A): void
     public @org.jetbrains.annotations.Nullable method get(): java.lang.Object
     public method getName(): java.lang.String
@@ -40,7 +40,7 @@ final class NoReceiverInCallableReferenceClassesKt$aBar$1 {
 }
 
 @kotlin.Metadata
-final class NoReceiverInCallableReferenceClassesKt$aFoo$1 {
+synthetic final class NoReceiverInCallableReferenceClassesKt$aFoo$1 {
     inner class NoReceiverInCallableReferenceClassesKt$aFoo$1
     method <init>(p0: A): void
     public final method getName(): java.lang.String