Switch pragma to 0.8.4 for all contracts in integration-tests and batch-submitter packages

integration-tests/contracts/ConstructorReverter.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 import { Reverter } from './Reverter.sol';
 

integration-tests/contracts/ERC20.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >=0.7.0 <0.8.0;
+pragma solidity ^0.8.4;
 
 contract ERC20 {
     event Transfer(address indexed _from, address indexed _to, uint256 _value);

integration-tests/contracts/OVMContextStorage.sol

 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 // Can't do this until the package is published.
 //import { iOVM_L1BlockNumber } from "@eth-optimism/contracts/iOVM_L1BlockNumber";

integration-tests/contracts/OVMMulticall.sol

@@ -18,7 +18,7 @@ copies or substantial portions of the Software.
 
 */
 
-pragma solidity ^0.7.0;
+pragma solidity ^0.8.4;
 
 pragma experimental ABIEncoderV2;
 

integration-tests/contracts/Proxy.sol

 // SPDX-License-Identifier: MIT
 
-pragma solidity >=0.6.0 <0.8.0;
+pragma solidity ^0.8.4;
 
 /**
  * @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM

integration-tests/contracts/Reverter.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 contract Reverter {
     string constant public revertMessage = "This is a simple reversion.";

integration-tests/contracts/SimpleStorage.sol

-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 contract ICrossDomainMessenger {
     address public xDomainMessageSender;

integration-tests/contracts/TestOOG.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 contract TestOOG {
     function runOutOfGas() public {

integration-tests/contracts/ValueCalls.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >=0.7.0;
+pragma solidity ^0.8.4;
 
 contract ValueContext {
     function getSelfBalance() external payable returns(uint256) {

integration-tests/hardhat.config.ts

@@ -16,7 +16,7 @@ const config: HardhatUserConfig = {
   mocha: {
     timeout: 50000,
   },
-  solidity: '0.7.6',
+  solidity: '0.8.4',
   gasReporter: {
     enabled: enableGasReport,
     currency: 'USD',

packages/batch-submitter/hardhat.config.ts

@@ -19,7 +19,7 @@ const config: HardhatUserConfig = {
     timeout: 50000,
   },
   solidity: {
-    version: '0.7.0',
+    version: '0.8.4',
     settings: {
       optimizer: {
         enabled: true,

packages/contracts/contracts/L2/predeploys/iOVM_L1BlockNumber.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >0.5.0 <0.8.0;
+pragma solidity ^0.8.4;
 
 /**
  * @title iOVM_L1BlockNumber

packages/contracts/contracts/libraries/constants/Lib_DefaultValues.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >0.5.0 <0.8.0;
+pragma solidity ^0.8.4;
 
 /**
  * @title Lib_DefaultValues

packages/contracts/contracts/libraries/constants/Lib_PredeployAddresses.sol

@@ -9,7 +9,7 @@ library Lib_PredeployAddresses {
     address internal constant L2_TO_L1_MESSAGE_PASSER = 0x4200000000000000000000000000000000000000;
     address internal constant L1_MESSAGE_SENDER = 0x4200000000000000000000000000000000000001;
     address internal constant DEPLOYER_WHITELIST = 0x4200000000000000000000000000000000000002;
-    address payable internal constant OVM_ETH = 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000;
+    address payable internal constant OVM_ETH = payable(0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000);
     // solhint-disable-next-line max-line-length
     address internal constant L2_CROSS_DOMAIN_MESSENGER = 0x4200000000000000000000000000000000000007;
     address internal constant LIB_ADDRESS_MANAGER = 0x4200000000000000000000000000000000000008;

packages/message-relayer/hardhat.config.ts

@@ -8,7 +8,7 @@ const config: HardhatUserConfig = {
     sources: './test/test-contracts',
   },
   solidity: {
-    version: '0.7.6',
+    version: '0.8.4',
   },
 }
 

packages/message-relayer/test/test-contracts/MockL2CrossDomainMessenger.sol

 // SPDX-License-Identifier: MIT
-pragma solidity >0.7.0 <0.9.0;
+pragma solidity ^0.8.4;
 pragma experimental ABIEncoderV2;
 
 contract MockL2CrossDomainMessenger {