Refactor ledger_entry RPC source code and tests (#5237)

This is a major refactor of LedgerEntry.cpp. It adds a number of helper functions to make the code easier to maintain.

It also splits up the ledger and ledger_entry tests into different files, and cleans up the ledger_entry tests to make them easier to write and maintain.

This refactor also caught a few bugs in some of the other RPC processing, so those are fixed along the way.

src/test/app/Vault_test.cpp

@@ -3028,18 +3028,6 @@ class Vault_test : public beast::unit_test::suite
                 "malformedRequest");
         }
 
-        {
-            testcase("RPC ledger_entry zero seq");
-            Json::Value jvParams;
-            jvParams[jss::ledger_index] = jss::validated;
-            jvParams[jss::vault][jss::owner] = issuer.human();
-            jvParams[jss::vault][jss::seq] = 0;
-            auto jvVault = env.rpc("json", "ledger_entry", to_string(jvParams));
-            BEAST_EXPECT(
-                jvVault[jss::result][jss::error].asString() ==
-                "malformedRequest");
-        }
-
         {
             testcase("RPC ledger_entry negative seq");
             Json::Value jvParams;

src/test/jtx/impl/xchain_bridge.cpp

@@ -44,10 +44,10 @@ bridge(
     Issue const& issuingChainIssue)
 {
     Json::Value jv;
-    jv[sfLockingChainDoor.getJsonName()] = lockingChainDoor.human();
-    jv[sfLockingChainIssue.getJsonName()] = to_json(lockingChainIssue);
-    jv[sfIssuingChainDoor.getJsonName()] = issuingChainDoor.human();
-    jv[sfIssuingChainIssue.getJsonName()] = to_json(issuingChainIssue);
+    jv[jss::LockingChainDoor] = lockingChainDoor.human();
+    jv[jss::LockingChainIssue] = to_json(lockingChainIssue);
+    jv[jss::IssuingChainDoor] = issuingChainDoor.human();
+    jv[jss::IssuingChainIssue] = to_json(issuingChainIssue);
     return jv;
 }
 
@@ -60,10 +60,10 @@ bridge_rpc(
     Issue const& issuingChainIssue)
 {
     Json::Value jv;
-    jv[sfLockingChainDoor.getJsonName()] = lockingChainDoor.human();
-    jv[sfLockingChainIssue.getJsonName()] = to_json(lockingChainIssue);
-    jv[sfIssuingChainDoor.getJsonName()] = issuingChainDoor.human();
-    jv[sfIssuingChainIssue.getJsonName()] = to_json(issuingChainIssue);
+    jv[jss::LockingChainDoor] = lockingChainDoor.human();
+    jv[jss::LockingChainIssue] = to_json(lockingChainIssue);
+    jv[jss::IssuingChainDoor] = issuingChainDoor.human();
+    jv[jss::IssuingChainIssue] = to_json(issuingChainIssue);
     return jv;
 }