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/ledger/Invariants_test.cpp

@@ -731,21 +731,6 @@ class Invariants_test : public beast::unit_test::suite
         using namespace test::jtx;
         testcase << "no zero escrow";
 
-        doInvariantCheck(
-            {{"Cannot return non-native STAmount as XRPAmount"}},
-            [](Account const& A1, Account const& A2, ApplyContext& ac) {
-                // escrow with nonnative amount
-                auto const sle = ac.view().peek(keylet::account(A1.id()));
-                if (!sle)
-                    return false;
-                auto sleNew = std::make_shared<SLE>(
-                    keylet::escrow(A1, (*sle)[sfSequence] + 2));
-                STAmount nonNative(A2["USD"](51));
-                sleNew->setFieldAmount(sfAmount, nonNative);
-                ac.view().insert(sleNew);
-                return true;
-            });
-
         doInvariantCheck(
             {{"XRP net change of -1000000 doesn't match fee 0"},
              {"escrow specifies invalid amount"}},