Remove xcm::v3 from assets-common nits (#4037)

This PR mainly removes `xcm::v3` stuff from `assets-common` to make it
more generic and facilitate the transition to newer XCM versions. Some
of the implementations here used hard-coded `xcm::v3::Location`, but now
it's up to the runtime to configure according to its needs.

Additional/consequent changes:
- `penpal` runtime uses now `xcm::latest::Location` for `pallet_assets`
as `AssetId`, because we don't care about migrations here
- it pretty much simplify xcm-emulator integration tests, where we don't
need now a lots of boilerplate conversions:
      ```
      v3::Location::try_from(...).expect("conversion works")`
      ```
- xcm-emulator tests
- split macro `impl_assets_helpers_for_parachain` to the
`impl_assets_helpers_for_parachain` and
`impl_foreign_assets_helpers_for_parachain` (avoids using hard-coded
`xcm::v3::Location`)

cumulus/parachains/runtimes/coretime/coretime-rococo/src/xcm_config.rs

@@ -77,7 +77,7 @@ pub type LocationToAccountId = (
 );
 
 /// Means for transacting the native currency on this chain.
-pub type CurrencyTransactor = FungibleAdapter<
+pub type FungibleTransactor = FungibleAdapter<
 	// Use this currency:
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
@@ -106,7 +106,7 @@ pub type RegionTransactor = NonFungibleAdapter<
 >;
 
 /// Means for transacting assets on this chain.
-pub type AssetTransactors = (CurrencyTransactor, RegionTransactor);
+pub type AssetTransactors = (FungibleTransactor, RegionTransactor);
 
 /// This is the type we use to convert an (incoming) XCM origin into a local `Origin` instance,
 /// ready for dispatching a transaction with XCM's `Transact`. There is an `OriginKind` that can