8305206: Add @spec tags in java.base/java.* (part 1)

Reviewed-by: alanb, naoto, darcy, lancea, dfuchs, iris, mchung

src/java.base/share/classes/java/lang/foreign/package-info.java

@@ -226,6 +226,7 @@
  * restricted methods is only granted to the modules listed by that option. If this option is not specified,
  * access to restricted methods is enabled for all modules, but access to restricted methods will result in runtime warnings.
  *
+ * @spec jni/index.html Java Native Interface Specification
  */
 package java.lang.foreign;