rpc: Register calls where they are defined

Split out methods to every module, apart from 'help' and 'stop' which
are implemented in rpcserver.cpp itself.

- This makes it easier to add or remove RPC commands - no longer everything that includes
    rpcserver.h has to be rebuilt when there's a change there.
- Cleans up `rpc/server.h` by getting rid of the huge cluttered list of function definitions.
- Removes most of the bitcoin-specific code from rpcserver.cpp and .h.

Continues #7307 for the non-wallet.

src/rpc/mining.cpp

@@ -781,3 +781,27 @@ UniValue estimatesmartpriority(const UniValue& params, bool fHelp)
     result.push_back(Pair("blocks", answerFound));
     return result;
 }
+
+static const CRPCCommand commands[] =
+{ //  category              name                      actor (function)         okSafeMode
+  //  --------------------- ------------------------  -----------------------  ----------
+    { "mining",             "getnetworkhashps",       &getnetworkhashps,       true  },
+    { "mining",             "getmininginfo",          &getmininginfo,          true  },
+    { "mining",             "prioritisetransaction",  &prioritisetransaction,  true  },
+    { "mining",             "getblocktemplate",       &getblocktemplate,       true  },
+    { "mining",             "submitblock",            &submitblock,            true  },
+
+    { "generating",         "generate",               &generate,               true  },
+    { "generating",         "generatetoaddress",      &generatetoaddress,      true  },
+
+    { "util",               "estimatefee",            &estimatefee,            true  },
+    { "util",               "estimatepriority",       &estimatepriority,       true  },
+    { "util",               "estimatesmartfee",       &estimatesmartfee,       true  },
+    { "util",               "estimatesmartpriority",  &estimatesmartpriority,  true  },
+};
+
+void RegisterMiningRPCCommands(CRPCTable &tableRPC)
+{
+    for (unsigned int vcidx = 0; vcidx < ARRAYLEN(commands); vcidx++)
+        tableRPC.appendCommand(commands[vcidx].name, &commands[vcidx]);
+}