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/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())