Fix key collision for child trie (#4162)

* In progress, runtime io must switch to future proof root +
child_specific (unique id) + u32 type.

* Switch interface, sr-io seems ok, rpc could use similar interface to
sr-io, genesis json broken if there is child trie in existing encoding
genesis.

* test from previous implementation.

* fix proving test.

* Restore Keyspacedb from other branch, only apply to child trie.

* Removing unneeded child_info from child root (child info are stored
if things changed, otherwhise the root does not change).

* Switch rpc to use same format as ext: more future proof.

* use root from child info for trie backend essence.

* Breaking long lines.

* Update doc and clean pr a bit.

* fix error type

* Restore removed doc on merge and update sr-io doc.

* Switch child storage api to use directly unique id, if managed id
where to be put in place, the api will change at this time.

* Clean deprecated host interface from child.

* Removing assertion on child info (can fail depending on root
memoization).

* merging child info in the overlay when possible.

* child iteration by prefix using child_info.

* Using ChainInfo in frame support. ChainInfo gets redesign to avoid
buffers allocation on every calls.

* Add length of root to the data of child info.

* comments

* Encode compact.

* Remove child info with root.

* Fix try_update condition.

* Comment Ext child root caching.

* Replace tuples by struct with field

* remove StorageTuple alias.

* Fix doc tests, and remove StorageOverlay and ChildStorageOverlay
aliases.

substrate/client/rpc/src/state/state_light.rs

@@ -236,6 +236,8 @@ impl<Block, F, B, E, RA> StateBackend<B, E, Block, RA> for LightState<Block, F,
 		&self,
 		_block: Option<Block::Hash>,
 		_child_storage_key: StorageKey,
+		_child_info: StorageKey,
+		_child_type: u32,
 		_prefix: StorageKey,
 	) -> FutureResult<Vec<StorageKey>> {
 		Box::new(result(Err(client_err(ClientError::NotAvailableOnLightClient))))
@@ -245,6 +247,8 @@ impl<Block, F, B, E, RA> StateBackend<B, E, Block, RA> for LightState<Block, F,
 		&self,
 		block: Option<Block::Hash>,
 		child_storage_key: StorageKey,
+		child_info: StorageKey,
+		child_type: u32,
 		key: StorageKey,
 	) -> FutureResult<Option<StorageData>> {
 		let block = self.block_or_best(block);
@@ -255,6 +259,8 @@ impl<Block, F, B, E, RA> StateBackend<B, E, Block, RA> for LightState<Block, F,
 					block,
 					header,
 					storage_key: child_storage_key.0,
+					child_info: child_info.0,
+					child_type,
 					keys: vec![key.0.clone()],
 					retry_count: Default::default(),
 				}).then(move |result| ready(result
@@ -275,10 +281,12 @@ impl<Block, F, B, E, RA> StateBackend<B, E, Block, RA> for LightState<Block, F,
 		&self,
 		block: Option<Block::Hash>,
 		child_storage_key: StorageKey,
+		child_info: StorageKey,
+		child_type: u32,
 		key: StorageKey,
 	) -> FutureResult<Option<Block::Hash>> {
 		Box::new(self
-			.child_storage(block, child_storage_key, key)
+			.child_storage(block, child_storage_key, child_info, child_type, key)
 			.and_then(|maybe_storage|
 				result(Ok(maybe_storage.map(|storage| Blake2Hasher::hash(&storage.0))))
 			)