Conflating Filtering and Identifying in XCM v0 NetworkId and MultiAsset

[apopiak]

I would like to raise an issue I see with XCM v0:
I see a difference between NetworkId and MultiAsset on the one hand and other enums/"identifiers" like MultiLocation or BodyPart. The latter separate the identifying and filtering parts. Identifying is done by the enum instance (e.g. a multilocation might be X2(Parachain(1), GeneralIndex(42))) while filtering is done in the XCM implementation (e.g. the IsTeleporter filter). This IMO is a good pattern.
NetworkId and MultiAsset combine an identifying function with a filter function within the enum which leads to non-filtering code having to manage the case when we get MultiAsset::AllFungible even though that is not its purpose. I think we should avoid this in v1 and separate filtering and identifying completely.

[apopiak]

related to #3168

[gavofyork]

Consider creating an XCM v1 tracking issue so when the time comes to move from v0 we have a single place with all the gripes.

[KiChjang]

With the introduction of MultiAssetFilter, I think this is fixed in v1 and later.