Update teleport_assets Extrinsics for Foreign Assets

[joepetrowski]

Right now the teleport_assets_* extrinsics use the teleported asset to BuyExecution on the destination chain. This can cause a problem if the teleported asset cannot be used for fee payment.

As an example, a parachain may be a trusted teleporter of its own native asset, but not for DOT, which is valid for fee payment on Asset Hub.

The extrinsic should be able to construct alternate XCM programs that would pay fees according to the parameters. Options include:

1. WithdrawAsset from the parachain's sovereign account on the destination chain and use that for BuyExecution.
2. Allow the deposit of reserve assets (e.g. DOT) prior to the ReceiveTeleportedAsset instruction.

Probably requires changes to the impl of XcmExecutor (e.g. in InitiateTeleportedAsset.

Originally posted by @joepetrowski in paritytech/cumulus#2935 (comment)

[bkontur]

We've tried to implement PoC for buying execution on destination from sovereign account for reserve_transfer_assets here, which seems almost the same as this issue. As PoC, we used AliasOrigin with one change in XcmExecutor,
which I also discussed here and here is another discussion from element,
but maybe it requires another approach.

[joepetrowski]

@acatangiu is this addressed by some of the other transfer changes you've made recently? Or should we leave it open?

[acatangiu]

This is possible now, but only if the Parachain trusts AH as reserve for DOT, so it can send AssetA and DOT directly to it (in same XCM message):

ParaA --Assets--> AH

where

Assets = [AssetA (teleport), DOT (reserve-withdraw)]

fees paid with DOT

---

If the Parachain does NOT trust AH as reserve, there is NO way to send both assets at once (in a single transfer), because they would have different routes, so two independent asynchronous messages with no ordering guarantee:

ParaA --------AssetA--------> AH
   |                           ^
   |                           |
   +--DOT--> Relaychain --DOT--+

if the transfer is fired for both assets at the same time, AssetA can arrive before the DOT and there is no way to control the order, so DOT cannot be used to pay for fees.

---

When Parachain trusts AH as reserve for DOT

Simply use pallet_xcm::transfer_assets() and it will do the rest.

Example: bidirectional transfers of [ForeignAsset, DOT] between Penpal and AH, using pallet_xcm::transfer_assets().

Or one can also explicitly define the "route" and "types" of transfer used with pallet_xcm::transfer_assets_using_type_and_then().

Example: bidirectional transfers of [ForeignAsset, DOT] between Penpal and AH, using pallet_xcm::transfer_assets_using_type_and_then().