Refactor transferCrossChain to support been extended by user in evm/UniversalNFTCore.sol

[andresaiello]

Right now transferCrossChain in UniversalNFTCore it's like this:

 function transferCrossChain(
        uint256 tokenId,
        address receiver,
        address destination
    ) external payable {
// code

then if you want to extend it and add custom code, you have to call super.transferCrossChain and as it's external will be expensive. I recommend to refactor like this:

 function transferCrossChain(
        uint256 tokenId,
        address receiver,
        address destination
    ) external payable {
_transferCrossChain(     tokenId,
        receiver,
        destination);
}

 function _transferCrossChain(
        uint256 tokenId,
        address receiver,
        address destination
    ) internal virtual{
// code
}

then if a developer wants to extend it it's just an internal call