Make all hierarchies of JavaAnnotationArgument sealed

compiler/resolution.common.jvm/src/org/jetbrains/kotlin/load/java/structure/impl/classFiles/Annotations.kt

@@ -279,7 +279,7 @@ class BinaryJavaAnnotationVisitor(
     }
 }
 
-abstract class PlainJavaAnnotationArgument(name: String?) : JavaAnnotationArgument {
+sealed class PlainJavaAnnotationArgument(name: String?) : JavaAnnotationArgument {
     override val name: Name? = name?.takeIf(Name::isValidIdentifier)?.let(Name::identifier)
 }
 

core/descriptors.runtime/src/org/jetbrains/kotlin/descriptors/runtime/structure/ReflectJavaAnnotationArguments.kt

@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.load.java.structure.*
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
 
-abstract class ReflectJavaAnnotationArgument(
+sealed class ReflectJavaAnnotationArgument(
     override val name: Name?
 ) : JavaAnnotationArgument {
     companion object Factory {