Improve Penpal runtime + emulated tests (#3543)

Issues addressed in this PR:
- Improve *Penpal* runtime:
- Properly handled received assets. Previously, it treated `(1, Here)`
as the local native currency, whereas it should be treated as a
`ForeignAsset`. This wasn't a great example of standard Parachain
behaviour, as no Parachain treats the system asset as the local
currency.
- Remove `AllowExplicitUnpaidExecutionFrom` the system. Again, this
wasn't a great example of standard Parachain behaviour.
- Move duplicated
`ForeignAssetFeeAsExistentialDepositMultiplierFeeCharger` to
`assets_common` crate.
- Improve emulated tests:
  - Update *Penpal* tests to new runtime.
- To simplify tests, register the reserve transferred, teleported, and
system assets in *Penpal* and *AssetHub* genesis. This saves us from
having to create the assets repeatedly for each test
- Add missing test case:
`reserve_transfer_assets_from_para_to_system_para`.
  - Cleanup.
- Prevent integration tests crates imports from being re-exported, as
they were polluting the `polkadot-sdk` docs.

There is still a test case missing for reserve transfers:
- Reserve transfer of system asset from *Parachain* to *Parachain*
trough *AssetHub*.
- This is not yet possible with `pallet-xcm` due to the reasons
explained in https://github.com/paritytech/polkadot-sdk/pull/3339

---------

Co-authored-by: command-bot <>

cumulus/parachains/integration-tests/emulated/common/src/lib.rs

@@ -21,17 +21,19 @@ pub use xcm_emulator;
 
 // Substrate
 use beefy_primitives::ecdsa_crypto::AuthorityId as BeefyId;
+use frame_support::parameter_types;
 use grandpa::AuthorityId as GrandpaId;
 use sp_authority_discovery::AuthorityId as AuthorityDiscoveryId;
 use sp_consensus_babe::AuthorityId as BabeId;
 use sp_core::{sr25519, storage::Storage, Pair, Public};
 use sp_runtime::{
-	traits::{IdentifyAccount, Verify},
+	traits::{AccountIdConversion, IdentifyAccount, Verify},
 	BuildStorage, MultiSignature,
 };
 
 // Polakdot
 use parachains_common::BlockNumber;
+use polkadot_parachain_primitives::primitives::Sibling;
 use polkadot_runtime_parachains::configuration::HostConfiguration;
 
 // Cumulus
@@ -49,6 +51,25 @@ pub const SAFE_XCM_VERSION: u32 = xcm::prelude::XCM_VERSION;
 
 type AccountPublic = <MultiSignature as Verify>::Signer;
 
+// This asset is added to AH as Asset and reserved transfer between Parachain and AH
+pub const RESERVABLE_ASSET_ID: u32 = 1;
+// This asset is added to AH as ForeignAsset and teleported between Penpal and AH
+pub const TELEPORTABLE_ASSET_ID: u32 = 2;
+
+pub const PENPAL_ID: u32 = 2000;
+pub const ASSETS_PALLET_ID: u8 = 50;
+
+parameter_types! {
+	pub PenpalTeleportableAssetLocation: xcm::v3::Location
+		= xcm::v3::Location::new(1, [
+				xcm::v3::Junction::Parachain(PENPAL_ID),
+				xcm::v3::Junction::PalletInstance(ASSETS_PALLET_ID),
+				xcm::v3::Junction::GeneralIndex(TELEPORTABLE_ASSET_ID.into()),
+			]
+		);
+	pub PenpalSiblingSovereigAccount: AccountId = Sibling::from(PENPAL_ID).into_account_truncating();
+}
+
 /// Helper function to generate a crypto pair from seed
 pub fn get_from_seed<TPublic: Public>(seed: &str) -> <TPublic::Pair as Pair>::Public {
 	TPublic::Pair::from_string(&format!("//{}", seed), None)