Move ResourceType-specific checks from ResourcePoolsImpl.validateAndMerge

[cljohnso]

The two checks in org.ehcache.core.config.ResourcePoolsImpl#validateAndMerge specific to OFFHEAP and DISK should be moved to those resource types -- the restrictions are defined as behavior of the type -- in order to remove the type-specific behavior from validateAndMerge logic.

The two checks at issue are:

    if(toBeUpdated.getResourceTypeSet().contains(ResourceType.Core.OFFHEAP)) {
      throw new UnsupportedOperationException("Updating OFFHEAP resource is not supported");
    }

    if(toBeUpdated.getResourceTypeSet().contains(ResourceType.Core.DISK)) {
      throw new UnsupportedOperationException("Updating DISK resource is not supported");
    }