Add JVM target bytecode version 21

Unfortunately, there are still problems with running JVM backend tests
with JVM target 21 because:

1) The D8 version that we use does not support bytecode version 21, and
   updating to a newer version requires to change JVM target of compiler
   tests to 11. This will be addressed separately when we enable JVM 21
   in tests-different-jdk.
2) Some tests are failing because of KT-60659 and KT-60770:
   - builtinStubMethods/bridgesForStubs/emptyStringListAdd.kt
   - jdk/stream.kt
   - regressions/kt528.kt

 #KT-60662 Fixed

compiler/testData/codegen/box/reflection/classes/nestedClasses.kt

@@ -26,7 +26,7 @@ fun box(): String {
     // Java interface with nested classes
     assertEquals(listOf("Entry"), nestedNames(java.util.Map::class))
     // Java class with nested classes
-    assertEquals(listOf("SimpleEntry", "SimpleImmutableEntry"), nestedNames(java.util.AbstractMap::class))
+    assertEquals(listOf("SimpleEntry", "SimpleImmutableEntry"), nestedNames(java.util.AbstractMap::class) - "ViewCollection")
 
     // Built-ins
     assertEquals(emptyList<String>(), nestedNames(Array<Any>::class))