chainHead: Backport error codes from spec (#2539)

This PR backports the error codes from the spec.

This relies on two specs for defining the error codes:
- Our rpc-spec-v2 https://github.com/paritytech/json-rpc-interface-spec.
- JSON-RPC spec https://www.jsonrpc.org/specification#error_object.

To better describe the error codes, they are divided into two separate
modules `rpc_spec_v2` and `json_rpc_spec` respectively.

The `InvalidSubscriptionID` and `FetchBlockHeader` are merged into the
JSON-RPC spec `INTERNAL_ERROR`.
While the other error codes are adjusted from spec.

Errors that are currently in use:
- -32801 block hash not reported by chainHead_follow or block hash has
been unpinned
- -32802 chainHead_follow started with withRuntime == false
- -32803 chainHead_follow did not generate an
operationWaitingForContinue event

The following are errors defined in the [JSON-RPC
spec](https://www.jsonrpc.org/specification#error_object):
- -32602 The provided parameter isn't one of the expected values, has
different format or is missing
- -32603 Internal server error

Note: Error `-32801` must be introduced and generated by the outstanding
https://github.com/paritytech/polkadot-sdk/issues/1505

Closes: https://github.com/paritytech/polkadot-sdk/issues/2530

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

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

@@ -198,7 +198,9 @@ where
 		let sub_id = match self.accept_subscription(&mut sink) {
 			Ok(sub_id) => sub_id,
 			Err(err) => {
-				sink.close(ChainHeadRpcError::InvalidSubscriptionID);
+				sink.close(ChainHeadRpcError::InternalError(
+					"Cannot generate subscription ID".into(),
+				));
 				return Err(err)
 			},
 		};
@@ -306,7 +308,7 @@ where
 		self.client
 			.header(hash)
 			.map(|opt_header| opt_header.map(|h| hex_string(&h.encode())))
-			.map_err(ChainHeadRpcError::FetchBlockHeader)
+			.map_err(|err| ChainHeadRpcError::InternalError(err.to_string()))
 			.map_err(Into::into)
 	}
 
@@ -393,7 +395,7 @@ where
 
 		// Reject subscription if with_runtime is false.
 		if !block_guard.has_runtime() {
-			return Err(ChainHeadRpcError::InvalidParam(
+			return Err(ChainHeadRpcError::InvalidRuntimeCall(
 				"The runtime updates flag must be set".to_string(),
 			)
 			.into())