add note on usage of twox hash (#13089)

substrate/frame/fast-unstake/src/lib.rs

@@ -147,6 +147,8 @@ pub mod pallet {
 	/// The map of all accounts wishing to be unstaked.
 	///
 	/// Keeps track of `AccountId` wishing to unstake and it's corresponding deposit.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	pub type Queue<T: Config> = CountedStorageMap<_, Twox64Concat, T::AccountId, BalanceOf<T>>;
 

substrate/frame/nomination-pools/src/lib.rs

@@ -1277,6 +1277,8 @@ pub mod pallet {
 	pub type MaxPoolMembersPerPool<T: Config> = StorageValue<_, u32, OptionQuery>;
 
 	/// Active members.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	pub type PoolMembers<T: Config> =
 		CountedStorageMap<_, Twox64Concat, T::AccountId, PoolMember<T>>;

substrate/frame/staking/src/pallet/mod.rs

@@ -292,6 +292,8 @@ pub mod pallet {
 	pub type Invulnerables<T: Config> = StorageValue<_, Vec<T::AccountId>, ValueQuery>;
 
 	/// Map from all locked "stash" accounts to the controller account.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	#[pallet::getter(fn bonded)]
 	pub type Bonded<T: Config> = StorageMap<_, Twox64Concat, T::AccountId, T::AccountId>;
@@ -320,12 +322,16 @@ pub mod pallet {
 	pub type Ledger<T: Config> = StorageMap<_, Blake2_128Concat, T::AccountId, StakingLedger<T>>;
 
 	/// Where the reward payment should be made. Keyed by stash.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	#[pallet::getter(fn payee)]
 	pub type Payee<T: Config> =
 		StorageMap<_, Twox64Concat, T::AccountId, RewardDestination<T::AccountId>, ValueQuery>;
 
 	/// The map from (wannabe) validator stash key to the preferences of that validator.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	#[pallet::getter(fn validators)]
 	pub type Validators<T: Config> =
@@ -353,6 +359,8 @@ pub mod pallet {
 	///
 	/// Lastly, if any of the nominators become non-decodable, they can be chilled immediately via
 	/// [`Call::chill_other`] dispatchable by anyone.
+	///
+	/// TWOX-NOTE: SAFE since `AccountId` is a secure hash.
 	#[pallet::storage]
 	#[pallet::getter(fn nominators)]
 	pub type Nominators<T: Config> =