refactor: Replace JSONRPCRequest fHelp field with mode field

No change in behavior

src/rpc/util.cpp

@@ -476,6 +476,18 @@ std::string RPCExamples::ToDescriptionString() const
     return m_examples.empty() ? m_examples : "\nExamples:\n" + m_examples;
 }
 
+UniValue RPCHelpMan::HandleRequest(const JSONRPCRequest& request)
+{
+    /*
+     * Check if the given request is valid according to this command or if
+     * the user is asking for help information, and throw help when appropriate.
+     */
+    if (request.mode == JSONRPCRequest::GET_HELP || !IsValidNumArgs(request.params.size())) {
+        throw std::runtime_error(ToString());
+    }
+    return m_fun(*this, request);
+}
+
 bool RPCHelpMan::IsValidNumArgs(size_t num_args) const
 {
     size_t num_required_args = 0;