Merge bitcoin/bitcoin#26074: refactor: Set RPCArg options with designated initializers

fa2c72dda0 rpc: Set RPCArg options with designated initializers (MacroFake)

Pull request description:

  For optional constructor arguments, use a new struct. This comes with two benefits:
  * Earlier unused optional arguments can be omitted
  * Designated initializers can be used

ACKs for top commit:
  stickies-v:
    re-ACK fa2c72dda0

Tree-SHA512: 2a0619548187cc7437fee2466ac4780746490622f202659f53641be01bc2a1fea4416d1a77f3e963bf7c4cce62899b61fab0b9683440cf82f68be44f63826658

src/wallet/rpc/spend.cpp

@@ -317,7 +317,7 @@ RPCHelpMan sendmany()
                 "\nSend multiple times. Amounts are double-precision floating point numbers." +
         HELP_REQUIRING_PASSPHRASE,
                 {
-                    {"dummy", RPCArg::Type::STR, RPCArg::Optional::NO, "Must be set to \"\" for backwards compatibility.", "\"\""},
+                    {"dummy", RPCArg::Type::STR, RPCArg::Optional::NO, "Must be set to \"\" for backwards compatibility.", RPCArgOptions{.oneline_description="\"\""}},
                     {"amounts", RPCArg::Type::OBJ_USER_KEYS, RPCArg::Optional::NO, "The addresses and amounts",
                         {
                             {"address", RPCArg::Type::AMOUNT, RPCArg::Optional::NO, "The bitcoin address is the key, the numeric amount (can be string) in " + CURRENCY_UNIT + " is the value"},
@@ -774,7 +774,7 @@ RPCHelpMan fundrawtransaction()
                              },
                         },
                         FundTxDoc()),
-                        "options"},
+                        RPCArgOptions{.oneline_description="options"}},
                     {"iswitness", RPCArg::Type::BOOL, RPCArg::DefaultHint{"depends on heuristic tests"}, "Whether the transaction hex is a serialized witness transaction.\n"
                         "If iswitness is not present, heuristic tests will be used in decoding.\n"
                         "If true, only witness deserialization will be tried.\n"
@@ -968,7 +968,7 @@ static RPCHelpMan bumpfee_helper(std::string method_name)
                     {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"unset"}, "The fee estimate mode, must be one of (case insensitive):\n"
                      "\"" + FeeModes("\"\n\"") + "\""},
                 },
-                "options"},
+                RPCArgOptions{.oneline_description="options"}},
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "", Cat(
@@ -1173,7 +1173,7 @@ RPCHelpMan send()
                     },
                 },
                 FundTxDoc()),
-                "options"},
+                RPCArgOptions{.oneline_description="options"}},
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "",
@@ -1281,7 +1281,7 @@ RPCHelpMan sendall()
                     },
                     FundTxDoc()
                 ),
-                "options"
+                RPCArgOptions{.oneline_description="options"}
             },
         },
         RPCResult{
@@ -1611,7 +1611,7 @@ RPCHelpMan walletcreatefundedpsbt()
                             },
                         },
                         FundTxDoc()),
-                        "options"},
+                        RPCArgOptions{.oneline_description="options"}},
                     {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
                 },
                 RPCResult{