Add support for transfer_assets_using_type_and_then extrinsic in pallet-xcm precompile

[Agusrodri]

What does it do?

This PR adds support for transfer_assets_using_type_and_then extrinsic in pallet-xcm precompile.

In total 4 new selectors were added to the pallet-xcm precompile interface:

• Selector 8425d893:

This function allows calling transfer_assets_using_type_and_then extrinsic (with assets being represented in Location format) by ONLY allowing combinations of LocalReserve, Teleport, and DestinationReserve transfer types. RemoteReserve type is not allowed here. It was decided to split the behavior in two functions for better params organization.

    /// @custom:selector 8425d893
    function transferAssetsUsingTypeAndThenLocation(
        Location memory dest,
        AssetLocationInfo[] memory assets,
        TransferType assetsTransferType,
        uint8 remoteFeesIdIndex,
        TransferType feesTransferType,
        bytes memory customXcmOnDest
    ) external;

• Selector fc19376c:

This function allows calling transfer_assets_using_type_and_then extrinsic (with assets being represented in Location format) through the RemoteReserve transfer type for both assets and fees. In this case, assets and fees MUST share the same reserve for the extrinsic to execute properly. This is being restricted by pallet-xcm, as it doesn't allow to send XCMs to separate chains, given that there is no guarantee of delivery order on final destination (more details here).

    /// @custom:selector fc19376c
    function transferAssetsUsingTypeAndThenLocation(
        Location memory dest,
        AssetLocationInfo[] memory assets,
        uint8 remoteFeesIdIndex,
        bytes memory customXcmOnDest,
        Location memory remoteReserve
    ) external;

• The other 2 remaining selectors (998093ee and aaecfc62) are identical to the ones described above. The only difference is that they receive the assets in Address format.

    /// @custom:selector 998093ee
    function transferAssetsUsingTypeAndThenAddress(
        Location memory dest,
        AssetAddressInfo[] memory assets,
        TransferType assetsTransferType,
        uint8 remoteFeesIdIndex,
        TransferType feesTransferType,
        bytes memory customXcmOnDest
    ) external;

    /// @custom:selector aaecfc62
    function transferAssetsUsingTypeAndThenAddress(
        Location memory dest,
        AssetAddressInfo[] memory assets,
        uint8 remoteFeesIdIndex,
        bytes memory customXcmOnDest,
        Location memory remoteReserve
    ) external;

Related upstream PRs

• pallet-xcm: add new extrinsic for asset transfers using explicit XCM transfer types paritytech/polkadot-sdk#3695
• pallet-xcm::transfer_assets_using_type_and_then() supports custom actions on destination paritytech/polkadot-sdk#4260

[librelois]

@Agusrodri Overall it's good, can you just explain in the solidity doc that customXcmOnDest should be SCALE encoded?