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/misc.cpp

@@ -396,3 +396,21 @@ UniValue setmocktime(const UniValue& params, bool fHelp)
 
     return NullUniValue;
 }
+
+static const CRPCCommand commands[] =
+{ //  category              name                      actor (function)         okSafeMode
+  //  --------------------- ------------------------  -----------------------  ----------
+    { "control",            "getinfo",                &getinfo,                true  }, /* uses wallet if enabled */
+    { "util",               "validateaddress",        &validateaddress,        true  }, /* uses wallet if enabled */
+    { "util",               "createmultisig",         &createmultisig,         true  },
+    { "util",               "verifymessage",          &verifymessage,          true  },
+
+    /* Not shown in help */
+    { "hidden",             "setmocktime",            &setmocktime,            true  },
+};
+
+void RegisterMiscRPCCommands(CRPCTable &tableRPC)
+{
+    for (unsigned int vcidx = 0; vcidx < ARRAYLEN(commands); vcidx++)
+        tableRPC.appendCommand(commands[vcidx].name, &commands[vcidx]);
+}