`fungibles` methods should not consume `AssetId`

[liamaharon]

Methods such as

polkadot-sdk/substrate/frame/support/src/traits/tokens/fungibles/regular.rs

Line 84 in cdacfb9

fn balance(asset: Self::AssetId, who: &AccountId) -> Self::Balance;

should take a ref rather than consume the AssetId.

It was probably written this way back when AssetIds were small and implemented Copy, but that's no longer the case with the increasing usage of XCM Locations as AssetIds.

All relevant fungibles methods should be updated, and unnecessary cloning of large types removed (e.g. in the asset-conversion pallet).

[bkontur]

Related issue for XCM Location: #3038

[dianpopa]

should be fixed by #4224