Remove xcm::v3 from assets-common nits

[bkontur]

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)

[franciscoaguirre]

Much better 🚀

[liamaharon]

Looks good. This looks like it may impact downstream parachains though, is R0 an appropriate label?

[bkontur]

Looks good. This looks like it may impact downstream parachains though, is R0 an appropriate label?

yes, you're right, I added the prdoc.

also waiting for merging #3695 first