APIv2(DeliverMax): add alias for Amount in Payment transactions (#4733)

Using the "Amount" field in Payment transactions can cause incorrect
interpretation. There continue to be problems from the use of this
field. "Amount" is rarely the correct field to use; instead,
"delivered_amount" (or "DeliveredAmount") should be used.

Rename the "Amount" field to "DeliverMax", a less misleading name. With
api_version: 2, remove the "Amount" field from Payment transactions.

- Input: "DeliverMax" in `tx_json` is an alias for "Amount"
  - sign
  - submit (in sign-and-submit mode)
  - submit_multisigned
  - sign_for
- Output: Add "DeliverMax" where transactions are provided by the API
  - ledger
  - tx
  - tx_history
  - account_tx
  - transaction_entry
  - subscribe (transactions stream)
- Output: Remove "Amount" from API version 2

Fix #3484

Fix #3902

src/test/rpc/Transaction_test.cpp

@@ -19,6 +19,7 @@
 
 #include <ripple/app/rdb/backend/SQLiteDatabase.h>
 #include <ripple/protocol/ErrorCodes.h>
+#include <ripple/protocol/STBase.h>
 #include <ripple/protocol/jss.h>
 #include <ripple/rpc/CTID.h>
 #include <optional>
@@ -692,6 +693,60 @@ class Transaction_test : public beast::unit_test::suite
         }
     }
 
+    void
+    testRequest(FeatureBitset features)
+    {
+        testcase("Test Request");
+
+        using namespace test::jtx;
+        using std::to_string;
+
+        const char* COMMAND = jss::tx.c_str();
+
+        Env env{*this};
+        Account const alice{"alice"};
+        Account const alie{"alie"};
+        Account const gw{"gw"};
+        auto const USD{gw["USD"]};
+
+        env.fund(XRP(1000000), alice, gw);
+        env.close();
+
+        // AccountSet
+        env(noop(alice));
+
+        // Payment
+        env(pay(alice, gw, XRP(100)));
+
+        std::shared_ptr<STTx const> txn = env.tx();
+        env.close();
+        std::shared_ptr<STObject const> meta =
+            env.closed()->txRead(env.tx()->getTransactionID()).second;
+
+        Json::Value expected = txn->getJson(JsonOptions::none);
+        expected[jss::DeliverMax] = expected[jss::Amount];
+
+        auto const result =
+            env.rpc(COMMAND, to_string(txn->getTransactionID()));
+        BEAST_EXPECT(result[jss::result][jss::status] == jss::success);
+
+        for (auto memberIt = expected.begin(); memberIt != expected.end();
+             memberIt++)
+        {
+            std::string const name = memberIt.memberName();
+            if (BEAST_EXPECT(result[jss::result].isMember(name)))
+            {
+                auto const received = result[jss::result][name];
+                BEAST_EXPECTS(
+                    received == *memberIt,
+                    "Transaction contains \n\"" + name + "\": "  //
+                        + to_string(received)                    //
+                        + " but expected "                       //
+                        + to_string(expected));
+            }
+        }
+    }
+
 public:
     void
     run() override
@@ -708,6 +763,7 @@ public:
         testRangeCTIDRequest(features);
         testCTIDValidation(features);
         testCTIDRPC(features);
+        testRequest(features);
     }
 };