Make offchain indexing work (#7940)

* Make offchain indexing work

This fixes some bugs with offchain indexing to make it actually working ;)

* Fix tests

* Fix browser build

* Update client/db/src/offchain.rs

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

* Remove seperation between prefix and key

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

substrate/utils/frame/benchmarking-cli/src/command.rs

@@ -62,7 +62,6 @@ impl BenchmarkCmd {
 
 		let genesis_storage = spec.build_storage()?;
 		let mut changes = Default::default();
-		let mut offchain_changes = Default::default();
 		let cache_size = Some(self.database_cache_size as usize);
 		let state = BenchmarkingState::<BB>::new(genesis_storage, cache_size)?;
 		let executor = NativeExecutor::<ExecDispatch>::new(
@@ -80,7 +79,6 @@ impl BenchmarkCmd {
 			&state,
 			None,
 			&mut changes,
-			&mut offchain_changes,
 			&executor,
 			"Benchmark_dispatch_benchmark",
 			&(