Recover transaction pool on light client (#3833)

* recover tx pool on light client

* revert local tests fix

* removed import renamings

* futures03::Future -> std::future::Future

* Update core/transaction-pool/graph/src/error.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* replace remove_from_ready with remove_invalid

* avoid excess hashing

* debug -> warn

* TransactionPool + BasicTransactionPool

* pause future tx reject when resubmitting

* bump impl_version to make CI happy

* and revert back local test fixes

* alter doc to restart CI

* Transaction::clone() -> Transaction::duplicate()

* transactions -> updated_tranasctions

* remove explicit consensus-common ref

* ::std:: -> std::

* manual set/unset flag -> calling clusore with given flag value

* removed comments

* removed force argument

* BestIterator -> Box<Iterator>

* separate crate for TxPool + Maintainer trait

* long line fix

* pos-merge fix

* fix benches compilation

* Rename txpoolapi to txpool_api

* Clean up.

* Finalize merge.

* post-merge fix

* Move transaction pool api to primitives directly.

* Consistent naming for txpool-runtime-api

* Warn about missing docs.

* Move  abstraction for offchain calls to tx-pool-api.

* Merge RPC instantiation.

* Update cargo.lock

* Post merge fixes.

* Avoid depending on client.

* Fix build

substrate/client/transaction-pool/graph/src/future.rs

@@ -227,6 +227,12 @@ impl<Hash: hash::Hash + Eq + Clone, Ex> FutureTransactions<Hash, Ex> {
 		self.waiting.values().map(|waiting| &*waiting.transaction)
 	}
 
+	/// Removes and returns all future transactions.
+	pub fn clear(&mut self) -> Vec<Arc<Transaction<Hash, Ex>>> {
+		self.wanted_tags.clear();
+		self.waiting.drain().map(|(_, tx)| tx.transaction).collect()
+	}
+
 	/// Returns number of transactions in the Future queue.
 	pub fn len(&self) -> usize {
 		self.waiting.len()