Add FixedPointOperand blanket implementation (#14634)

* bound `Balance` to `FixedPointOperand`

* ".git/.scripts/commands/fmt/fmt.sh"

* clean up code

* Apply suggestions from code review

Co-authored-by: Gavin Wood <gavin@parity.io>

* wip

* add blanket `FixedPointOperand` impl

* update nis CurrencyBalance

* remove CheckedNeg bound

---------

Co-authored-by: command-bot <>
Co-authored-by: Gavin Wood <gavin@parity.io>

substrate/frame/assets/src/types.rs

@@ -22,7 +22,7 @@ use frame_support::{
 	pallet_prelude::*,
 	traits::{fungible, tokens::ConversionToAssetBalance},
 };
-use sp_runtime::{traits::Convert, FixedPointNumber, FixedPointOperand, FixedU128};
+use sp_runtime::{traits::Convert, FixedPointNumber, FixedU128};
 
 pub(super) type DepositBalanceOf<T, I = ()> =
 	<<T as Config<I>>::Currency as Currency<<T as SystemConfig>::AccountId>>::Balance;
@@ -293,8 +293,6 @@ where
 	T: Config<I>,
 	I: 'static,
 	CON: Convert<BalanceOf<F, T>, AssetBalanceOf<T, I>>,
-	BalanceOf<F, T>: FixedPointOperand + Zero,
-	AssetBalanceOf<T, I>: FixedPointOperand + Zero,
 {
 	type Error = ConversionError;