feat(ctb): add legacy fn to L2StandardBridge

Adds a missing legacy function to the L2StandardBridge.

packages/contracts-bedrock/.gas-snapshot

@@ -163,11 +163,11 @@ L2OutputOracleUpgradeable_Test:test_initValuesOnProxy_succeeds() (gas: 26093)
 L2OutputOracleUpgradeable_Test:test_initializeImpl_alreadyInitialized_reverts() (gas: 15149)
 L2OutputOracleUpgradeable_Test:test_initializeProxy_alreadyInitialized_reverts() (gas: 20131)
 L2OutputOracleUpgradeable_Test:test_upgrading_succeeds() (gas: 180413)
-L2StandardBridge_Test:test_finalizeBridgeETH_incorrectValue_reverts() (gas: 23788)
-L2StandardBridge_Test:test_finalizeBridgeETH_sendToMessenger_reverts() (gas: 23927)
-L2StandardBridge_Test:test_finalizeBridgeETH_sendToSelf_reverts() (gas: 23838)
-L2StandardBridge_Test:test_finalizeDeposit_succeeds() (gas: 89396)
-L2StandardBridge_Test:test_initialize_succeeds() (gas: 10537)
+L2StandardBridge_Test:test_finalizeBridgeETH_incorrectValue_reverts() (gas: 23843)
+L2StandardBridge_Test:test_finalizeBridgeETH_sendToMessenger_reverts() (gas: 23982)
+L2StandardBridge_Test:test_finalizeBridgeETH_sendToSelf_reverts() (gas: 23893)
+L2StandardBridge_Test:test_finalizeDeposit_succeeds() (gas: 89473)
+L2StandardBridge_Test:test_initialize_succeeds() (gas: 24270)
 L2StandardBridge_Test:test_receive_succeeds() (gas: 131905)
 L2StandardBridge_Test:test_withdrawTo_succeeds() (gas: 344660)
 L2StandardBridge_Test:test_withdraw_insufficientValue_reverts() (gas: 19630)

packages/contracts-bedrock/contracts/L2/L2StandardBridge.sol

@@ -138,6 +138,16 @@ contract L2StandardBridge is StandardBridge, Semver {
         emit DepositFinalized(_l1Token, _l2Token, _from, _to, _amount, _extraData);
     }
 
+    /**
+     * @custom:legacy
+     * @notice Retrieves the access of the corresponding L1 bridge contract.
+     *
+     * @return Address of the corresponding L1 bridge contract.
+     */
+    function l1TokenBridge() external view returns (address) {
+        return address(OTHER_BRIDGE);
+    }
+
     /**
      * @custom:legacy
      * @notice Internal function to a withdrawal from L2 to L1 to a target account on L1.

packages/contracts-bedrock/contracts/test/L2StandardBridge.t.sol

@@ -16,7 +16,7 @@ contract L2StandardBridge_Test is Bridge_Initializer {
 
     function test_initialize_succeeds() external {
         assertEq(address(L2Bridge.messenger()), address(L2Messenger));
-
+        assertEq(L1Bridge.l2TokenBridge(), address(L2Bridge));
         assertEq(address(L2Bridge.OTHER_BRIDGE()), address(L1Bridge));
     }