rpc: fix "trusted" description in TransactionDescriptionString

The helps for RPCs gettransaction, listtransactions, and
listsinceblock returned by TransactionDescriptionString()
state that the "trusted" boolean field is only present if the
transaction is trusted and safe to spend from.

The "trusted" boolean field is in fact returned by
WalletTxToJSON() when the transaction has 0 confirmations,
or negative confirmations, if conflicted, and it can be
true or false.

This commit updates TransactionDescriptionString() to a
more accurate description for "trusted" and updates the
existing line of test coverage to fail more helpfully.

src/wallet/rpcwallet.cpp

@@ -1389,7 +1389,8 @@ static const std::vector<RPCResult> TransactionDescriptionString()
     return{{RPCResult::Type::NUM, "confirmations", "The number of confirmations for the transaction. Negative confirmations means the\n"
                "transaction conflicted that many blocks ago."},
            {RPCResult::Type::BOOL, "generated", /* optional */ true, "Only present if transaction only input is a coinbase one."},
-           {RPCResult::Type::BOOL, "trusted", /* optional */ true, "Only present if we consider transaction to be trusted and so safe to spend from."},
+           {RPCResult::Type::BOOL, "trusted", /* optional */ true, "Whether we consider the transaction to be trusted and safe to spend from.\n"
+                "Only present when the transaction has 0 confirmations (or negative confirmations, if conflicted)."},
            {RPCResult::Type::STR_HEX, "blockhash", /* optional */ true, "The block hash containing the transaction."},
            {RPCResult::Type::NUM, "blockheight", /* optional */ true, "The block height containing the transaction."},
            {RPCResult::Type::NUM, "blockindex", /* optional */ true, "The index of the transaction in the block that includes it."},
@@ -1407,7 +1408,7 @@ static const std::vector<RPCResult> TransactionDescriptionString()
            {RPCResult::Type::NUM_TIME, "timereceived", "The time received expressed in " + UNIX_EPOCH_TIME + "."},
            {RPCResult::Type::STR, "comment", /* optional */ true, "If a comment is associated with the transaction, only present if not empty."},
            {RPCResult::Type::STR, "bip125-replaceable", "(\"yes|no|unknown\") Whether this transaction could be replaced due to BIP125 (replace-by-fee);\n"
-               "may be unknown for unconfirmed transactions not in the mempool"}};
+               "may be unknown for unconfirmed transactions not in the mempool."}};
 }
 
 static RPCHelpMan listtransactions()

test/functional/wallet_import_rescan.py

@@ -99,7 +99,7 @@ class Variant(collections.namedtuple("Variant", "call data address_type rescan p
             assert_equal(tx["label"], self.label)
             assert_equal(tx["txid"], txid)
             assert_equal(tx["confirmations"], 1 + current_height - confirmation_height)
-            assert_equal("trusted" not in tx, True)
+            assert "trusted" not in tx
 
             address, = [ad for ad in addresses if txid in ad["txids"]]
             assert_equal(address["address"], self.address["address"])