Companion for #13352 (#2180)

* Assets balances

* Update docs

* AssetsApi with MultiLocation as preparation for multi pallet_assets instances (#2187)

* AssetsApi with MultiLocation for Westmint + assets-common

* AssetsApi with MultiLocation for Statemine/t

* typo

* typo for check-docs job

* WIP: AssetsApi return MultiAsset instead of (MultiLocation, Balance)

* WIP: assets_api + conversion refactor

* WIP: assets_api + conversion refactor

* Finished asset runtimes

* Refactor AssetsApi to FungiblesApi

* Refactor

* Fix check-rust-docs

* Removed todo

* Fix check-rust-doc

* Update parachains/runtimes/assets/common/Cargo.toml

Co-authored-by: Bastian Köcher <git@kchr.de>

* update lockfile for {"substrate", "polkadot"}

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Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: parity-processbot <>
Co-authored-by: Bastian Köcher <git@kchr.de>