Replace system config Index for Nonce (#14290)

* replace Index by Nonce

* replace Index by Nonce

* replace Index by Nonce

* replace Index by Nonce

* replace Index by Nonce

* wip

* remove index in lieu of nonce

* wip

* remove accountnonce in lieu of nonce

* add minor improvement

* rebase and merge conflicts

substrate/frame/system/benchmarking/src/mock.rs

@@ -23,7 +23,7 @@ use codec::Encode;
 use sp_runtime::{traits::IdentityLookup, BuildStorage};
 
 type AccountId = u64;
-type AccountIndex = u32;
+type Nonce = u32;
 
 type Block = frame_system::mocking::MockBlock<Test>;
 
@@ -40,7 +40,7 @@ impl frame_system::Config for Test {
 	type BlockLength = ();
 	type DbWeight = ();
 	type RuntimeOrigin = RuntimeOrigin;
-	type Index = AccountIndex;
+	type Nonce = Nonce;
 	type RuntimeCall = RuntimeCall;
 	type Hash = sp_core::H256;
 	type Hashing = ::sp_runtime::traits::BlakeTwo256;