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/src/genesis.rs

@@ -53,7 +53,7 @@ mod tests {
 		runtime::{Hash, Transfer, Block, BlockNumber, Header, Digest},
 		AccountKeyring, Sr25519Keyring,
 	};
-	use primitives::{Blake2Hasher, map};
+	use primitives::Blake2Hasher;
 	use hex_literal::*;
 
 	native_executor_instance!(
@@ -154,8 +154,7 @@ mod tests {
 			vec![AccountKeyring::One.into(), AccountKeyring::Two.into()],
 			1000,
 			None,
-			map![],
-			map![],
+			Default::default(),
 		).genesis_map();
 		let genesis_hash = insert_genesis_block(&mut storage);
 
@@ -183,8 +182,7 @@ mod tests {
 			vec![AccountKeyring::One.into(), AccountKeyring::Two.into()],
 			1000,
 			None,
-			map![],
-			map![],
+			Default::default(),
 		).genesis_map();
 		let genesis_hash = insert_genesis_block(&mut storage);
 
@@ -212,8 +210,7 @@ mod tests {
 			vec![AccountKeyring::One.into(), AccountKeyring::Two.into()],
 			68,
 			None,
-			map![],
-			map![],
+			Default::default(),
 		).genesis_map();
 		let genesis_hash = insert_genesis_block(&mut storage);