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/test-utils/runtime/client/src/block_builder_ext.rs

@@ -49,11 +49,7 @@ impl<'a, A, B> BlockBuilderExt
 	for sc_block_builder::BlockBuilder<'a, substrate_test_runtime::Block, A, B>
 where
 	A: ProvideRuntimeApi<substrate_test_runtime::Block> + 'a,
-	A::Api: BlockBuilderApi<substrate_test_runtime::Block>
-		+ ApiExt<
-			substrate_test_runtime::Block,
-			StateBackend = backend::StateBackendFor<B, substrate_test_runtime::Block>,
-		>,
+	A::Api: BlockBuilderApi<substrate_test_runtime::Block> + ApiExt<substrate_test_runtime::Block>,
 	B: backend::Backend<substrate_test_runtime::Block>,
 {
 	fn push_transfer(

substrate/test-utils/runtime/src/lib.rs

@@ -816,10 +816,8 @@ fn test_witness(proof: StorageProof, root: crate::Hash) {
 	let db: sp_trie::MemoryDB<crate::Hashing> = proof.into_memory_db();
 	let backend = sp_state_machine::TrieBackendBuilder::<_, crate::Hashing>::new(db, root).build();
 	let mut overlay = sp_state_machine::OverlayedChanges::default();
-	let mut cache = sp_state_machine::StorageTransactionCache::<_, _>::default();
 	let mut ext = sp_state_machine::Ext::new(
 		&mut overlay,
-		&mut cache,
 		&backend,
 		#[cfg(feature = "std")]
 		None,