Merge #21035: Remove pointer cast in CRPCTable::dumpArgMap

9048c58e10 Remove pointer cast in CRPCTable::dumpArgMap (Russell Yanofsky)
14f3d9b908 refactor: Add RPC server ExecuteCommands function (Russell Yanofsky)
6158a6d397 refactor: Replace JSONRPCRequest fHelp field with mode field (Russell Yanofsky)

Pull request description:

  This change is needed to fix the `rpc_help.py` test failing in #10102: https://cirrus-ci.com/task/5469433013469184?command=ci#L2275

  The [`CRPCTable::dumpArgMap`](16b784d953/src/rpc/server.cpp (L492)) method currently works by casting RPC `unique_id` integer field to a function pointer, and then calling it. The `unique_id` field wasn't supposed to be used this way (it's meant to be used to detect RPC aliases) and as a result, this code segfaults in the `rpc_help.py` test in multiprocess PR #10102 because wallet RPC functions aren't directly accessible from the node process.

  Fix this by adding a new `GET_ARGS` RPC request mode to retrieve argument information similar to the way the `GET_HELP` mode retrieves help information.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

ACKs for top commit:
  MarcoFalke:
    re-ACK 9048c58e10 👑

Tree-SHA512: cd1a01c1daa5bde2c2455b63548371ee4cf39688313969ad2016d9a0fd4344102e3fd43034058f253364518e9632d57cf21abffad0d6a2c0c94b7a6921cbe615

src/wallet/rpcwallet.cpp

@@ -96,7 +96,7 @@ bool GetWalletNameFromJSONRPCRequest(const JSONRPCRequest& request, std::string&
 
 std::shared_ptr<CWallet> GetWalletForJSONRPCRequest(const JSONRPCRequest& request)
 {
-    CHECK_NONFATAL(!request.fHelp);
+    CHECK_NONFATAL(request.mode == JSONRPCRequest::EXECUTE);
     std::string wallet_name;
     if (GetWalletNameFromJSONRPCRequest(request, wallet_name)) {
         std::shared_ptr<CWallet> pwallet = GetWallet(wallet_name);