Allow block IDs of 0 and non-contiguous subdomain IDs

[aprilnovak]

MOOSE technically allows blocks to have a subdomain ID of 0, but Aurora will throw this error:

if(blk < 1 || blk > maxBlockID){
          std::string errmsg="Block ID "+std::to_string(blk)+" for material "+mat
            +" is inconsistent with mesh (max subdomains = "
            +std::to_string(maxBlockID)+")";
            mooseError(errmsg);
        }

[aprilnovak]

More generally, Aurora seems to require that block IDs in the [Mesh] are ordered as 1, 2, 3, ... sequentially. However, MOOSE itself does not mandate this and use any unsigned integer values to represent the subdomains.