Give spring-core access to jdk.unsupported for Objenesis support on WildFly

[marschall]

Add a Dependencies manifest entry with the value jdk.unsupported to
spring-core.

Objenesis repackaged in Spring Core needs access to sun.reflect.ReflectionFactory located in the jdk.unsupported module. WildFly by default restricts applications from accessing the jdk.unsupported module (WFCORE-4055). This leads to obscure exceptions like #21528. In our case the default constructor of a Spring Batch job scoped bean could not be found. This was confusing because the bean had an autowired non-default constructor. The problem and solution were not obvious to us.

To give Objenesis in spring-core access to the jdk.unsupported module users need to do either of the following:

• Add a Dependencies manifest entry to the application or module itself
• Use jboss-deployment-structure.xml

As Spring Core uses a repackaged Objenesis we can instead add the Dependencies manifest header to spring-core itself making things "just work"(tm) for Spring users on WildFly.

[marschall]

This change maintains compatibility with JDK 8.

[wilkinsona]

This change seems to break applications deployed to old versions of Wildfly. See spring-projects/spring-boot#24686 for details.