Child trie storage proof (#2433)

* proof on child trie

* higher level api for child storage proof

* boilerplate for proof from light fetch

* actually check proof on light fetch

* Do not break former encoding

* tabify

* tabify2

* Add child trie root tx to full_storage_root transaction.

* Shorten long lines.

* Temp rename for audit

* Make full_storage a trait method

* Name back and replace some code with full_storage where it looks fine.

* fix indentations, remove unused import

* flush child root to top when calculated

* impl +1

substrate/core/state-machine/src/overlayed_changes.rs

@@ -159,19 +159,6 @@ impl OverlayedChanges {
 		}
 	}
 
-	/// Sync the child storage root.
-	pub(crate) fn sync_child_storage_root(&mut self, storage_key: &[u8], root: Option<Vec<u8>>) {
-		let entry = self.prospective.top.entry(storage_key.to_vec()).or_default();
-		entry.value = root;
-
-		if let Some((Some(extrinsics), _)) = self.prospective.children.get(storage_key) {
-			for extrinsic in extrinsics {
-				entry.extrinsics.get_or_insert_with(Default::default)
-					.insert(*extrinsic);
-			}
-		}
-	}
-
 	/// Clear child storage of given storage key.
 	///
 	/// NOTE that this doesn't take place immediately but written into the prospective