chainHead: Add support for storage closest merkle descendant #14818 (#1153)

This PR adds support for fetching the closest merkle value of some key.


Builds on top of
- https://github.com/paritytech/trie/pull/199

Migrates https://github.com/paritytech/substrate/pull/14818 to the
monorepo.
Closes: https://github.com/paritytech/substrate/issues/14550
Closes: https://github.com/paritytech/polkadot-sdk/issues/1506

// @paritytech/subxt-team

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

substrate/client/rpc-spec-v2/src/chain_head/chain_head.rs

@@ -27,7 +27,7 @@ use crate::{
 		api::ChainHeadApiServer,
 		chain_head_follow::ChainHeadFollower,
 		error::Error as ChainHeadRpcError,
-		event::{FollowEvent, MethodResponse, OperationError, StorageQuery, StorageQueryType},
+		event::{FollowEvent, MethodResponse, OperationError, StorageQuery},
 		hex_string,
 		subscription::{SubscriptionManagement, SubscriptionManagementError},
 	},
@@ -329,19 +329,10 @@ where
 		let items = items
 			.into_iter()
 			.map(|query| {
-				if query.query_type == StorageQueryType::ClosestDescendantMerkleValue {
-					// Note: remove this once all types are implemented.
-					return Err(ChainHeadRpcError::InvalidParam(
-						"Storage query type not supported".into(),
-					))
-				}
-
-				Ok(StorageQuery {
-					key: StorageKey(parse_hex_param(query.key)?),
-					query_type: query.query_type,
-				})
+				let key = StorageKey(parse_hex_param(query.key)?);
+				Ok(StorageQuery { key, query_type: query.query_type })
 			})
-			.collect::<Result<Vec<_>, _>>()?;
+			.collect::<Result<Vec<_>, ChainHeadRpcError>>()?;
 
 		let child_trie = child_trie
 			.map(|child_trie| parse_hex_param(child_trie))