Native: improve ClassCastException message for local classes

Previously it was like "null cannot be cast to MyObject" or
"MyObject cannot be cast to null", because `KClass.qualifiedName` is
`null` for local classes (including anonymous ones).

Use `KClass.toString()` instead, for both object actual dynamic type
and cast target type. This string representation is generally more
meaningful for such cases, and contains useful details for local
classes.

compiler/testData/codegen/box/casts/nativeCCEMessage/castToLocalClass.kt

@@ -0,0 +1,20 @@
+// TARGET_BACKEND: NATIVE
+
+class MyObject
+
+// Test infrastructure can move declarations to a package. So we need a prefix for class names in exception messages:
+val p = MyObject::class.qualifiedName!!.removeSuffix("MyObject")
+
+fun box(): String {
+    class MyLocalObject
+    try {
+        MyObject() as MyLocalObject
+    } catch (e: Throwable) {
+        if (e !is ClassCastException) return "fail 1: $e"
+        if (e.message != "class ${p}MyObject cannot be cast to class ${p}box\$MyLocalObject") return "fail 2: ${e.message}"
+
+        return "OK"
+    }
+
+    return "fail 3"
+}