Refactory of Fork-Tree data structure (#11228)

* Iterative version of some fork-tree methods

* Prune doesn't require its generic args to be 'clone'

* Fork-tree import and drain-filter iterative implementations

* Fork-tree map iterative implementation

* Optimization of some operations, e.g. rebalance only when required

* Destructuring assignments not supported yet by stable rustc 1.57

* Safe implementation of 'map' and 'drain_filter' methods

* Remove dummy comment

* Trigger CI pipeline

* Test map for multi-root fork-tree and refactory of `find_node_index_where`

* Fix find node index with predicate

* Nits

* Tree traversal algorithm is not specified

* Move unspecified tree traversal warning to 'map'

* Immutable 'drain_filter' predicate

* Apply suggestions from code review

* Remove double mapping

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

substrate/client/finality-grandpa/src/authorities.rs

@@ -229,7 +229,7 @@ where
 	where
 		F: Fn(&H, &H) -> Result<bool, E>,
 	{
-		let mut filter = |node_hash: &H, node_num: &N, _: &PendingChange<H, N>| {
+		let filter = |node_hash: &H, node_num: &N, _: &PendingChange<H, N>| {
 			if number >= *node_num &&
 				(is_descendent_of(node_hash, &hash).unwrap_or_default() || *node_hash == hash)
 			{
@@ -245,7 +245,7 @@ where
 		};
 
 		// Remove standard changes.
-		let _ = self.pending_standard_changes.drain_filter(&mut filter);
+		let _ = self.pending_standard_changes.drain_filter(&filter);
 
 		// Remove forced changes.
 		self.pending_forced_changes