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/cli/jvm/wrongJvmTargetVersion.out

@@ -1,3 +1,3 @@
 error: unknown JVM target version: 1.5
-Supported versions: 1.6, 1.8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
+Supported versions: 1.6, 1.8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
 COMPILATION_ERROR