JVM_IR: refactor ToArrayLowering and make matching more precise

* If `toArray` is inherited from Java, it may take an argument or
    return a value of a flexible type, which looks nullable in IR;
  * The returned array may also have `out` variance of the type
    argument;
  * `Array<T>` is not the same as `Array<Any?>` if `T` is neither `Any`
    nor `in Something`, so presence of `toArray(): Array<T>` does not
    mean we don't need to generate a new `toArray`.

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

@@ -0,0 +1,51 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// 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
+
+public abstract class MyListWithCustomToArray<E> extends java.util.AbstractList<E> {
+    public Object[] toArray() {
+        return new Object[]{null};
+    }
+
+    public <T> T[] toArray(T[] a) {
+        return a;
+    }
+}
+
+// FILE: a.kt
+class MyList<T>(val list: List<T>): java.util.AbstractList<T>() {
+    override fun get(index: Int): T = list[index]
+
+    override val size: Int
+        get() = list.size
+}
+
+class MyListSubclass<T>(val list: List<T>): MyListWithCustomToArray<T>() {
+    override fun get(index: Int): T = list[index]
+
+    override val size: Int
+        get() = list.size
+}
+
+class MyCollection<T>(val list: List<T>) : Collection<T> by list {
+    fun toArray(): Array<Int?> =
+        arrayOfNulls<Int>(0)
+}
+
+fun box(): String {
+    val list1 = MyList(listOf(2, 3, 9)) as java.util.Collection<*>
+    list1.toArray().contentToString().let { if (it != "[2, 3, 9]") return "fail 1: $it" }
+    list1.toArray(arrayOfNulls<Int>(0)).contentToString().let { if (it != "[2, 3, 9]") return "fail 2: $it" }
+
+    val list2 = MyListSubclass(listOf(2, 3, 9)) as java.util.Collection<*>
+    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<*>
+    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"
+}