Watch existing extrinsics RPC (#3873)

* Transaction pool watch intristics.

* Track extrinsic rpc methods.

* Test for pool watcher.

* Track extrinsic rpc test.

* Fix rpc naming.

* review fixes

* Update jsonrpc and use une subcription.

* Naming and dependencies.

substrate/core/rpc/api/src/author/mod.rs

@@ -67,7 +67,7 @@ pub trait AuthorApi<Hash, BlockHash> {
 		subscribe,
 		name = "author_submitAndWatchExtrinsic"
 	)]
-	fn watch_extrinsic(&self,
+	fn submit_and_watch_extrinsic(&self,
 		metadata: Self::Metadata,
 		subscriber: Subscriber<Status<Hash, BlockHash>>,
 		bytes: Bytes
@@ -83,4 +83,16 @@ pub trait AuthorApi<Hash, BlockHash> {
 		metadata: Option<Self::Metadata>,
 		id: SubscriptionId
 	) -> Result<bool>;
+
+	/// Watch multiple extrinsics (own or from network)
+	#[pubsub(
+		subscription = "author_extrinsicUpdate",
+		subscribe,
+		name = "author_watchExtrinsic"
+	)]
+	fn watch_extrinsic(&self,
+    	metadata: Self::Metadata,
+		subscriber: Subscriber<Status<Hash, BlockHash>>,
+	    hash: Hash,
+	);
 }