pallet-xcm: enhance reserve_transfer_assets to support remote reserves (#1672)

## Motivation

`pallet-xcm` is the main user-facing interface for XCM functionality,
including assets manipulation functions like `teleportAssets()` and
`reserve_transfer_assets()` calls.

While `teleportAsset()` works both ways, `reserve_transfer_assets()`
works only for sending reserve-based assets to a remote destination and
beneficiary when the reserve is the _local chain_.

## Solution

This PR enhances `pallet_xcm::(limited_)reserve_withdraw_assets` to
support transfers when reserves are other chains.
This will allow complete, **bi-directional** reserve-based asset
transfers user stories using `pallet-xcm`.

Enables following scenarios:
- transferring assets with local reserve (was previously supported iff
asset used as fee also had local reserve - now it works in all cases),
- transferring assets with reserve on destination,
- transferring assets with reserve on remote/third-party chain (iff
assets and fees have same remote reserve),
- transferring assets with reserve different than the reserve of the
asset to be used as fees - meaning can be used to transfer random asset
with local/dest reserve while using DOT for fees on all involved chains,
even if DOT local/dest reserve doesn't match asset reserve,
- transferring assets with any type of local/dest reserve while using
fees which can be teleported between involved chains.

All of the above is done by pallet inner logic without the user having
to specify which scenario/reserves/teleports/etc. The correct scenario
and corresponding XCM programs are identified, and respectively, built
automatically based on runtime configuration of trusted teleporters and
trusted reserves.

#### Current limitations:
- while `fees` and "non-fee" `assets` CAN have different reserves (or
fees CAN be teleported), the remaining "non-fee" `assets` CANNOT, among
themselves, have different reserve locations (this is also implicitly
enforced by `MAX_ASSETS_FOR_TRANSFER=2`, but this can be safely
increased in the future).
- `fees` and "non-fee" `assets` CANNOT have **different remote**
reserves (this could also be supported in the future, but adds even more
complexity while possibly not being worth it - we'll see what the future
holds).

Fixes https://github.com/paritytech/polkadot-sdk/issues/1584
Fixes https://github.com/paritytech/polkadot-sdk/issues/2055

---------

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>

cumulus/scripts/bridges_rococo_westend.sh

@@ -301,9 +301,21 @@ case "$1" in
           0 \
           "Unlimited"
       ;;
+  withdraw-reserve-assets-from-asset-hub-rococo-local)
+      ensure_polkadot_js_api
+      # send back only 100000000000 wrappedWNDs to Alice account on AHW
+      limited_reserve_transfer_assets \
+          "ws://127.0.0.1:9910" \
+          "//Alice" \
+          "$(jq --null-input '{ "V3": { "parents": 2, "interior": { "X2": [ { "GlobalConsensus": "Westend" }, { "Parachain": 1000 } ] } } }')" \
+          "$(jq --null-input '{ "V3": { "parents": 0, "interior": { "X1": { "AccountId32": { "id": [212, 53, 147, 199, 21, 253, 211, 28, 97, 20, 26, 189, 4, 169, 159, 214, 130, 44, 133, 88, 133, 76, 205, 227, 154, 86, 132, 231, 165, 109, 162, 125] } } } } }')" \
+          "$(jq --null-input '{ "V3": [ { "id": { "Concrete": { "parents": 2, "interior": { "X1": { "GlobalConsensus": "Westend" } } } }, "fun": { "Fungible": 140000000000 } } ] }')" \
+          0 \
+          "Unlimited"
+      ;;
   reserve-transfer-assets-from-asset-hub-westend-local)
       ensure_polkadot_js_api
-      # send WOCs to Alice account on AHR
+      # send WNDs to Alice account on AHR
       limited_reserve_transfer_assets \
           "ws://127.0.0.1:9010" \
           "//Alice" \
@@ -313,6 +325,18 @@ case "$1" in
           0 \
           "Unlimited"
       ;;
+  withdraw-reserve-assets-from-asset-hub-westend-local)
+      ensure_polkadot_js_api
+      # send back only 100000000000 wrappedROCs to Alice account on AHR
+      limited_reserve_transfer_assets \
+          "ws://127.0.0.1:9010" \
+          "//Alice" \
+          "$(jq --null-input '{ "V3": { "parents": 2, "interior": { "X2": [ { "GlobalConsensus": "Rococo" }, { "Parachain": 1000 } ] } } }')" \
+          "$(jq --null-input '{ "V3": { "parents": 0, "interior": { "X1": { "AccountId32": { "id": [212, 53, 147, 199, 21, 253, 211, 28, 97, 20, 26, 189, 4, 169, 159, 214, 130, 44, 133, 88, 133, 76, 205, 227, 154, 86, 132, 231, 165, 109, 162, 125] } } } } }')" \
+          "$(jq --null-input '{ "V3": [ { "id": { "Concrete": { "parents": 2, "interior": { "X1": { "GlobalConsensus": "Rococo" } } } }, "fun": { "Fungible": 100000000000 } } ] }')" \
+          0 \
+          "Unlimited"
+      ;;
   claim-rewards-bridge-hub-rococo-local)
       ensure_polkadot_js_api
       # bhwd -> [62, 68, 77, 64] -> 0x62687764
@@ -360,7 +384,9 @@ case "$1" in
           - init-asset-hub-westend-local
           - init-bridge-hub-westend-local
           - reserve-transfer-assets-from-asset-hub-rococo-local
+          - withdraw-reserve-assets-from-asset-hub-rococo-local
           - reserve-transfer-assets-from-asset-hub-westend-local
+          - withdraw-reserve-assets-from-asset-hub-westend-local
           - claim-rewards-bridge-hub-rococo-local
           - claim-rewards-bridge-hub-westend-local";
     exit 1