Migrate all JDK 15 related tests to JDK 17

compiler/testData/codegen/boxModernJdk/testsWithJava17/sealed/sealedJavaClassViaKotlinReflection.kt

@@ -0,0 +1,21 @@
+// WITH_REFLECT
+// FILE: Base.java
+public sealed class Base permits O, K {}
+
+// FILE: O.java
+public final class O extends Base {}
+
+// FILE: K.java
+public non-sealed class K extends Base {}
+
+// FILE: main.kt
+
+fun box(): String {
+    val klass = Base::class
+    if (!klass.isSealed) return "Error: Base is not sealed"
+    if (klass.isAbstract) return "Error: Base is not abstract"
+    return klass.sealedSubclasses
+        .joinToString("") { it.simpleName ?: "_No name provided_" }
+        .takeIf { it.isNotBlank() }
+        ?: "_No sealed subclasses found_"
+}