JVM IR: allow custom toArray to have any array type

To avoid breaking Java source compatibility. This problem can be fixed
later once JVM IR is stabilized.

 #KT-43111 Fixed

compiler/testData/codegen/box/toArray/toArrayFromJava.kt

@@ -1,6 +1,4 @@
 // TARGET_BACKEND: JVM
-// The old backend thinks `toArray(): Array<Int?>` is the same as `toArray(): Array<Any?>`
-// IGNORE_BACKEND: JVM
 // WITH_RUNTIME
 // FILE: MyListWithCustomToArray.java
 
@@ -29,7 +27,7 @@ class MyListSubclass<T>(val list: List<T>): MyListWithCustomToArray<T>() {
         get() = list.size
 }
 
-class MyCollection<T>(val list: List<T>) : Collection<T> by list {
+class MyCollectionWithCustomIntToArray<T>(val list: List<T>) : Collection<T> by list {
     fun toArray(): Array<Int?> =
         arrayOfNulls<Int>(0)
 }
@@ -43,8 +41,13 @@ fun box(): String {
     list2.toArray().contentToString().let { if (it != "[null]") return "fail 3: $it" }
     list2.toArray(arrayOfNulls<Int>(1)).contentToString().let { if (it != "[null]") return "fail 4: $it" }
 
-    val list3 = MyCollection(listOf(2, 3, 9)) as java.util.Collection<*>
+    val list3 = MyCollectionWithCustomIntToArray(listOf(2, 3, 9)) as java.util.Collection<*>
+    /*
+    // This fails with AbstractMethodError at the moment because of a bug where the backend doesn't check the array element type
+    // of the return type when looking for an implementation of the non-generic parameterless `toArray`.
+    // See `FunctionDescriptor.isNonGenericToArray`, `IrSimpleFunction.isNonGenericToArray` and KT-43111.
     list3.toArray().contentToString().let { if (it != "[2, 3, 9]") return "fail 5: $it" }
     list3.toArray(arrayOfNulls<Int>(0)).contentToString().let { if (it != "[2, 3, 9]") return "fail 6: $it" }
+     */
     return "OK"
 }