RPCs that return detailed information about mempool entries (e.g. `getmempoolentry` and `getrawmempool(verbose=True)` include the fields `fee`, `modifiedfee`, `descendantfees`, and `ancestorfees` which were marked as "DEPRECATED" and replaced with a `fees` object field in #12240 (since v0.17).

We should remove these fields, but first, properly deprecate them using `-deprecatedrpc`.

#### Useful skills:

- basic understanding of Bitcoin Core RPC interface

#### Want to work on this issue?

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

{RPCResult::Type::NUM, "nchaintx", "the number of transactions in the chain up to and including the base block"},
                }
        },
        RPCExamples{
            HelpExampleCli("dumptxoutset", "utxo.dat")
        },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    const fs::path path = fsbridge::AbsPathJoin(gArgs.GetDataDirNet(), fs::u8path(request.params[0].get_str()));
    
    
    const fs::path temppath = fsbridge::AbsPathJoin(gArgs.GetDataDirNet(), fs::u8path(request.params[0].get_str() + ".incomplete"));
    if (fs::exists(path)) {
        throw JSONRPCError(
            RPC_INVALID_PARAMETER,
            path.u8string() + " already exists. If you are sure this is what you want, "
            "move it out of the way first");
    }
    FILE* file{fsbridge::fopen(temppath, "wb")};
    CAutoFile afile{file, SER_DISK, CLIENT_VERSION};
    NodeContext& node = EnsureAnyNodeContext(request.context);
    UniValue result = CreateUTXOSnapshot(
        node, node.chainman->ActiveChainstate(), afile, path, temppath);
    fs::rename(temppath, path);
    result.pushKV("path", path.u8string());
    return result;
},
    };
}
UniValue CreateUTXOSnapshot(