Add support for XLS-85 Token Escrow (#5185)

- Specification: https://github.com/XRPLF/XRPL-Standards/pull/272
- Amendment: `TokenEscrow`
- Enables escrowing of IOU and MPT tokens in addition to native XRP.
- Allows accounts to lock issued tokens (IOU/MPT) in escrow objects, with support for freeze, authorization, and transfer rates.
- Adds new ledger fields (`sfLockedAmount`, `sfIssuerNode`, etc.) to track locked balances for IOU and MPT escrows.
- Updates EscrowCreate, EscrowFinish, and EscrowCancel transaction logic to support IOU and MPT assets, including proper handling of trustlines and MPT authorization, transfer rates, and locked balances.
- Enforces invariant checks for escrowed IOU/MPT amounts.
- Extends GatewayBalances RPC to report locked (escrowed) balances.

src/test/rpc/AccountLines_test.cpp

@@ -573,21 +573,6 @@ public:
         env.fund(XRP(10000), alice, becky, gw1);
         env.close();
 
-        // A couple of helper lambdas
-        auto escrow = [&env](
-                          Account const& account,
-                          Account const& to,
-                          STAmount const& amount) {
-            Json::Value jv;
-            jv[jss::TransactionType] = jss::EscrowCreate;
-            jv[jss::Account] = account.human();
-            jv[jss::Destination] = to.human();
-            jv[jss::Amount] = amount.getJson(JsonOptions::none);
-            NetClock::time_point finish = env.now() + 1s;
-            jv[sfFinishAfter.jsonName] = finish.time_since_epoch().count();
-            return jv;
-        };
-
         auto payChan = [](Account const& account,
                           Account const& to,
                           STAmount const& amount,
@@ -623,8 +608,10 @@ public:
         env.close();
 
         // Escrow, in each direction
-        env(escrow(alice, becky, XRP(1000)));
-        env(escrow(becky, alice, XRP(1000)));
+        env(escrow::create(alice, becky, XRP(1000)),
+            escrow::finish_time(env.now() + 1s));
+        env(escrow::create(becky, alice, XRP(1000)),
+            escrow::finish_time(env.now() + 1s));
 
         // Pay channels, in each direction
         env(payChan(alice, becky, XRP(1000), 100s, alice.pk()));

src/test/rpc/AccountSet_test.cpp

@@ -99,6 +99,12 @@ public:
                     // is tested elsewhere.
                     continue;
                 }
+                if (flag == asfAllowTrustLineLocking)
+                {
+                    // These flags are part of the AllowTokenLocking amendment
+                    // and are tested elsewhere
+                    continue;
+                }
 
                 if (std::find(goodFlags.begin(), goodFlags.end(), flag) !=
                     goodFlags.end())