EmulatorPkg: Add NetworkPkg/NetworkPkg.dec as the package dependency
    
    NetLib will be moved from MdeModulePkg and NetworkPkg.
    So, the module that consumes NetLib need to depend on NetworkPkg.dec.
    
    Signed-off-by: Liming Gao <liming.gao@intel.com>
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Andrew Fish <afish@apple.com>
    Cc: Ray Ni <ray.ni@intel.com>
    Reviewed-by: Ray Ni <ray.ni@intel.com>