[NFTs] Offchain mint (#13158)

* Allow to mint with the pre-signed signatures

* Another try

* WIP: test encoder

* Fix the deposits

* Refactoring + tests + benchmarks

* Add sp-core/runtime-benchmarks

* Remove sp-core from dev deps

* Enable full_crypto for benchmarks

* Typo

* Fix

* Update frame/nfts/src/mock.rs

Co-authored-by: Squirrel <gilescope@gmail.com>

* ".git/.scripts/commands/bench/bench.sh" pallet dev pallet_nfts

* Add docs

* Add attributes into the pre-signed object & track the deposit owner for attributes

* Update docs

* ".git/.scripts/commands/bench/bench.sh" pallet dev pallet_nfts

* Add the number of attributes provided to weights

* Apply suggestions

* Remove dead code

* Remove Copy

* Fix docs

* Update frame/nfts/src/lib.rs

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Update frame/nfts/src/lib.rs

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

---------

Co-authored-by: Squirrel <gilescope@gmail.com>
Co-authored-by: command-bot <>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/nfts/src/common_functions.rs

@@ -17,7 +17,7 @@
 
 //! Various pieces of common functionality.
 
-use super::*;
+use crate::*;
 
 impl<T: Config<I>, I: 'static> Pallet<T, I> {
 	/// Get the owner of the item, if the item exists.