Make offchain tx pool creation reusable (#14230)

* Make offchain tx pool creation reusable

Introduces an `OffchainTransactionPoolFactory` for creating offchain transactions pools that can be
registered in the runtime externalities context. This factory will be required for a later pr to
make the creation of offchain transaction pools easier.

* Update client/transaction-pool/api/src/lib.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

---------

Co-authored-by: Anton <anton.kalyaev@gmail.com>

substrate/client/transaction-pool/src/lib.rs

@@ -52,8 +52,8 @@ use std::{
 use graph::{ExtrinsicHash, IsValidator};
 use sc_transaction_pool_api::{
 	error::Error as TxPoolError, ChainEvent, ImportNotificationStream, MaintainedTransactionPool,
-	PoolFuture, PoolStatus, ReadyTransactions, TransactionFor, TransactionPool, TransactionSource,
-	TransactionStatusStreamFor, TxHash,
+	OffchainTransactionPoolFactory, PoolFuture, PoolStatus, ReadyTransactions, TransactionFor,
+	TransactionPool, TransactionSource, TransactionStatusStreamFor, TxHash,
 };
 use sp_core::traits::SpawnEssentialNamed;
 use sp_runtime::{
@@ -397,7 +397,9 @@ where
 		));
 
 		// make transaction pool available for off-chain runtime calls.
-		client.execution_extensions().register_transaction_pool(&pool);
+		client
+			.execution_extensions()
+			.register_transaction_pool_factory(OffchainTransactionPoolFactory::new(&pool));
 
 		pool
 	}
@@ -421,7 +423,7 @@ where
 
 	fn submit_local(
 		&self,
-		at: &BlockId<Self::Block>,
+		at: Block::Hash,
 		xt: sc_transaction_pool_api::LocalTransactionFor<Self>,
 	) -> Result<Self::Hash, Self::Error> {
 		use sp_runtime::{
@@ -430,7 +432,11 @@ where
 
 		let validity = self
 			.api
-			.validate_transaction_blocking(at, TransactionSource::Local, xt.clone())?
+			.validate_transaction_blocking(
+				&BlockId::hash(at),
+				TransactionSource::Local,
+				xt.clone(),
+			)?
 			.map_err(|e| {
 				Self::Error::Pool(match e {
 					TransactionValidityError::Invalid(i) => TxPoolError::InvalidTransaction(i),
@@ -441,7 +447,7 @@ where
 		let (hash, bytes) = self.pool.validated_pool().api().hash_and_length(&xt);
 		let block_number = self
 			.api
-			.block_id_to_number(at)?
+			.block_id_to_number(&BlockId::hash(at))?
 			.ok_or_else(|| error::Error::BlockIdConversion(format!("{:?}", at)))?;
 
 		let validated = ValidatedTransaction::valid_at(