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/test-utils/runtime/src/system.rs

@@ -361,16 +361,16 @@ mod tests {
 		];
 		TestExternalities::new_with_code(
 			WASM_BINARY,
-			(
-				map![
+			primitives::storage::Storage {
+				top: map![
 					twox_128(b"latest").to_vec() => vec![69u8; 32],
 					twox_128(b"sys:auth").to_vec() => authorities.encode(),
 					blake2_256(&AccountKeyring::Alice.to_raw_public().to_keyed_vec(b"balance:")).to_vec() => {
 						vec![111u8, 0, 0, 0, 0, 0, 0, 0]
 					}
 				],
-				map![],
-			)
+				children: map![],
+			},
 		)
 	}