RFR: 8218731: SA: Use concrete class the as return type of VMObjectFactory.newObject

[Stefan Karlsson]

Hi all,

I propose this simple change to use the concrete class as the return 
type of VMObjectFactory.newObject.

https://cr.openjdk.java.net/~stefank/8218731/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8218731

This allows us to specify the class only once when calling newObject. 
For example, now we can use:
return VMObjectFactory.newObject(ZPhysicalMemoryManager.class, 
physicalAddr);

Instead of having to write:
        return 
(ZPhysicalMemoryManager)VMObjectFactory.newObject(ZPhysicalMemoryManager.class, 
physicalAddr);

Thanks,
StefanK