contracts-bedrock: OptimismMintableERC20 immutables

Turn the constructor args into immutables. There isn't
a real reason for them to be in storage. The legacy
tokens can have the constructor args held in storage
and it shouldn't make a difference.

packages/contracts-bedrock/.gas-snapshot

@@ -108,22 +108,22 @@ L2OutputOracleUpgradeable_Test:test_cannotInitImpl() (gas: 15171)
 L2OutputOracleUpgradeable_Test:test_cannotInitProxy() (gas: 20152)
 L2OutputOracleUpgradeable_Test:test_initValuesOnProxy() (gas: 26095)
 L2OutputOracleUpgradeable_Test:test_upgrading() (gas: 180457)
-L2StandardBridge_Test:test_cannotWithdrawEthWithoutSendingIt() (gas: 21749)
+L2StandardBridge_Test:test_cannotWithdrawEthWithoutSendingIt() (gas: 19643)
 L2StandardBridge_Test:test_finalizeBridgeETH_incorrectValueReverts() (gas: 23733)
 L2StandardBridge_Test:test_finalizeBridgeETH_sendToMessengerReverts() (gas: 23960)
 L2StandardBridge_Test:test_finalizeBridgeETH_sendToSelfReverts() (gas: 23793)
-L2StandardBridge_Test:test_finalizeDeposit() (gas: 93522)
+L2StandardBridge_Test:test_finalizeDeposit() (gas: 89316)
 L2StandardBridge_Test:test_initialize() (gas: 10536)
 L2StandardBridge_Test:test_receive() (gas: 131820)
-L2StandardBridge_Test:test_withdraw() (gas: 347362)
-L2StandardBridge_Test:test_withdrawTo() (gas: 348091)
+L2StandardBridge_Test:test_withdraw() (gas: 343912)
+L2StandardBridge_Test:test_withdrawTo() (gas: 344641)
 L2StandardBridge_Test:test_withdraw_onlyEOA() (gas: 251816)
 L2ToL1MessagePasserTest:test_burn() (gas: 112530)
 L2ToL1MessagePasserTest:test_initiateWithdrawal_fromContract() (gas: 70246)
 L2ToL1MessagePasserTest:test_initiateWithdrawal_fromEOA() (gas: 75764)
 LegacyERC20ETH_Test:test_approve() (gas: 10723)
 LegacyERC20ETH_Test:test_burn() (gas: 10592)
-LegacyERC20ETH_Test:test_crossDomain() (gas: 10518)
+LegacyERC20ETH_Test:test_crossDomain() (gas: 6306)
 LegacyERC20ETH_Test:test_decreaseAllowance() (gas: 10679)
 LegacyERC20ETH_Test:test_increaseAllowance() (gas: 10667)
 LegacyERC20ETH_Test:test_metadata() (gas: 15391)
@@ -131,18 +131,18 @@ LegacyERC20ETH_Test:test_mint() (gas: 10649)
 LegacyERC20ETH_Test:test_transfer() (gas: 10733)
 LegacyERC20ETH_Test:test_transferFrom() (gas: 12887)
 LegacyMessagePasser_Test:test_LegacyMessagePasser_passMessageToL1_Succeeds() (gas: 34519)
-OptimismMintableERC20_Test:test_bridge() (gas: 9733)
-OptimismMintableERC20_Test:test_burn() (gas: 52772)
-OptimismMintableERC20_Test:test_burnRevertsFromNotBridge() (gas: 13241)
+OptimismMintableERC20_Test:test_bridge() (gas: 7624)
+OptimismMintableERC20_Test:test_burn() (gas: 51012)
+OptimismMintableERC20_Test:test_burnRevertsFromNotBridge() (gas: 11141)
 OptimismMintableERC20_Test:test_erc165_supportsInterface() (gas: 7696)
-OptimismMintableERC20_Test:test_l1Token() (gas: 9728)
-OptimismMintableERC20_Test:test_l2Bridge() (gas: 9739)
-OptimismMintableERC20_Test:test_mint() (gas: 65709)
-OptimismMintableERC20_Test:test_mintRevertsFromNotBridge() (gas: 13198)
-OptimismMintableERC20_Test:test_remoteToken() (gas: 9733)
+OptimismMintableERC20_Test:test_l1Token() (gas: 7622)
+OptimismMintableERC20_Test:test_l2Bridge() (gas: 7633)
+OptimismMintableERC20_Test:test_mint() (gas: 63609)
+OptimismMintableERC20_Test:test_mintRevertsFromNotBridge() (gas: 11098)
+OptimismMintableERC20_Test:test_remoteToken() (gas: 7624)
 OptimismMintableTokenFactory_Test:test_bridge() (gas: 7577)
-OptimismMintableTokenFactory_Test:test_createStandardL2Token() (gas: 1109783)
-OptimismMintableTokenFactory_Test:test_createStandardL2TokenSameTwice() (gas: 2205709)
+OptimismMintableTokenFactory_Test:test_createStandardL2Token() (gas: 1083647)
+OptimismMintableTokenFactory_Test:test_createStandardL2TokenSameTwice() (gas: 2153437)
 OptimismMintableTokenFactory_Test:test_createStandardL2TokenShouldRevertIfRemoteIsZero() (gas: 9413)
 OptimismPortalUpgradeable_Test:test_initialize_cannotInitImpl_reverts() (gas: 10791)
 OptimismPortalUpgradeable_Test:test_initialize_cannotInitProxy_reverts() (gas: 15767)

packages/contracts-bedrock/contracts/universal/OptimismMintableERC20.sol

@@ -16,12 +16,12 @@ contract OptimismMintableERC20 is IOptimismMintableERC20, ILegacyMintableERC20,
     /**
      * @notice Address of the corresponding version of this token on the remote chain.
      */
-    address public remoteToken;
+    address immutable public remoteToken;
 
     /**
      * @notice Address of the StandardBridge on this network.
      */
-    address public bridge;
+    address immutable public bridge;
 
     /**
      * @notice Emitted whenever tokens are minted for an account.