Set StateBackend::Transaction to PrefixedMemoryDB (#14612)

* Yep

* Try to get it working everywhere

* Make `from_raw_storage` start with an empty db

* More fixes!

* Make everything compile

* Fix `child_storage_root`

* Fix after merge

* Cleanups

* Update primitives/state-machine/src/overlayed_changes/mod.rs

Co-authored-by: Davide Galassi <davxy@datawok.net>

* Review comments

* Fix issues

* Silence warning

* FMT

* Clippy

---------

Co-authored-by: Davide Galassi <davxy@datawok.net>

substrate/utils/frame/benchmarking-cli/src/block/bench.rs

@@ -77,7 +77,7 @@ where
 		+ UsageProvider<Block>
 		+ BlockBackend<Block>
 		+ HeaderBackend<Block>,
-	C::Api: ApiExt<Block, StateBackend = BA::State> + BlockBuilderApi<Block>,
+	C::Api: ApiExt<Block> + BlockBuilderApi<Block>,
 {
 	/// Returns a new [`Self`] from the arguments.
 	pub fn new(client: Arc<C>, params: BenchmarkParams) -> Self {

substrate/utils/frame/benchmarking-cli/src/block/cmd.rs

@@ -90,7 +90,7 @@ impl BlockCmd {
 			+ StorageProvider<Block, BA>
 			+ UsageProvider<Block>
 			+ HeaderBackend<Block>,
-		C::Api: ApiExt<Block, StateBackend = BA::State> + BlockBuilderApi<Block>,
+		C::Api: ApiExt<Block> + BlockBuilderApi<Block>,
 	{
 		// Put everything in the benchmark type to have the generic types handy.
 		Benchmark::new(client, self.params.clone()).run()