MDB class Java heap leak on application stop

[tkburroughs]

Describe the bug
There is a reference from the Liberty message-driven bean (MDB) code to the application's MDB class through a pool that does not appear to be cleaned on application stop. See the following reference chain:

'- enterpriseBeanClass com.ibm.ejs.container.MessageEndpointFactoryImpl @ 0x8d630f50
   '- ivMessageEnpointHandlerFactory com.ibm.ws.ejbcontainer.mdb.MessageEndpointHandlerPool @ 0x8d6307c8
      '- discardStrategy com.ibm.ws.ejbcontainer.util.PoolImplThreadSafe @ 0x8d6301e0
         '- [3] java.lang.Object[10] @ 0x8677de20
            '- elementData java.util.ArrayList @ 0x817b8f10
               '- pools com.ibm.ws.ejbcontainer.util.PoolManagerImpl @ 0x817b8ee8
                  '- poolManager com.ibm.ejs.container.EJSContainer @ 0x80f024e0

Steps to Reproduce
Start and then stop an application with a message-driven bean. Repeating these actions will increase the Java heap.

Expected behavior
All references to applications classes are released when an application is stopped.

Diagnostic information:

• Affected feature(s) : mdb-3.2; mdb 4-0

Additional context
None.

[tkburroughs]

Fixes #PH50062