Refund unused tokens to the sender on ZetaChain

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When a transfer (EVM to EVM or ZetaChain to EVM) fails, the unused tokens must be returned to the sender on ZetaChain inside onRevert:

standard-contracts/contracts/nft/contracts/zetachain/UniversalNFT.sol

Lines 228 to 237 in 1a36032

	function onRevert(RevertContext calldata context) external onlyGateway {
	(uint256 tokenId, string memory uri, address sender) = abi.decode(
	context.revertMessage,
	(uint256, string, address)
	);
	_safeMint(sender, tokenId);
	_setTokenURI(tokenId, uri);
	emit TokenTransferReverted(sender, tokenId, uri);
	}

For ZetaChain to EVM transfers this is not that important, because the contract charges only the required amount and refunds unused tokens back before executing transferCrossChain.

But for EVM to EVM transfers this is important, because a sender may supply more tokens than required. In a successful transfer the tokens are refunded on the destination chain, but in case of revert the excess tokens (RevertContext.amount) are lost.

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The question is, should the tokens be swapped to ZETA or refunded as ZRC-20? In case of a revert, the sender might want to transfer the token to a different chain, and for that they'd need ZETA.