Inner classes of generic classes can't extend Throwable

Do it in the same way as Java: prohibit inner classes (including
anonymous inner classes) capturing type parameters from outer classes
(but not outer methods) extending Throwable.

See KT-17981:
- Deprecated in 1.2
- Error in 1.3

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -69,6 +69,7 @@ enum class LanguageFeature(
     NestedClassesInEnumEntryShouldBeInner(KOTLIN_1_3),
     ProhibitDataClassesOverridingCopy(KOTLIN_1_3),
     RestrictionOfWrongAnnotationsWithUseSiteTargetsOnTypes(KOTLIN_1_3),
+    ProhibitInnerClassesOfGenericClassExtendingThrowable(KOTLIN_1_3),
 
     // Experimental features