Improve Thread safeness of LocalTxConnectionEventListener

[escay]

Improve Thread safeness of LocalTxConnectionEventListener to prevent errors like:

Caused by: java.lang.NullPointerException: Cannot invoke "com.sun.enterprise.resource.ResourceHandle.getResourceSpec()" because "resource" is null
        at com.sun.enterprise.resource.pool.PoolManagerImpl.resourceClosed(PoolManagerImpl.java:367)
        at com.sun.enterprise.resource.listener.LocalTxConnectionEventListener.connectionClosed(LocalTxConnectionEventListener.java:58)
        at com.sun.gjc.spi.ManagedConnectionImpl.connectionClosed(ManagedConnectionImpl.java:735)
        at com.sun.gjc.spi.base.ConnectionHolder.close(ConnectionHolder.java:193)
        at com.sun.gjc.spi.jdbc40.ConnectionHolder40.close(ConnectionHolder40.java:590)

to improve the contents of the associatedHandles Map to be more threadsafe.

As part of the investigation of #24805 I ran into similar Payara issue: payara/Payara#3029 which I logged in the past. This was fixed in payara/Payara@c09e8aa

Fix idea:

• improve calls to "private IdentityHashMap associatedHandles;" to be more thread safe, preventing poolManager.resourceClosed(handle); to be called if another thread already updated associatedHandles.
• refactor com.sun.enterprise.resource.ConnectorXAResource.resetAssociation() logic -> so no external classes are updating associatedHandles anymore, making updating the associatedHandles the responsibility of class LocalTxConnectionEventListener