8309937: Add @sealedGraph for some Panama FFM interfaces

Reviewed-by: mcimadamore

src/java.base/share/classes/java/lang/foreign/GroupLayout.java

@@ -37,6 +37,7 @@ import jdk.internal.javac.PreviewFeature;
  * @implSpec
  * This class is immutable, thread-safe and <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>.
  *
+ * @sealedGraph
  * @since 19
  */
 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)