Improve events usability by indexing helpful params

packages/contracts/contracts/L1/messaging/OVM_L1CrossDomainMessenger.sol

@@ -212,7 +212,7 @@ contract OVM_L1CrossDomainMessenger is
             _gasLimit
         );
 
-        emit SentMessage(xDomainCalldata);
+        emit SentMessage(_target, _message, nonce, _gasLimit);
     }
 
     /**

packages/contracts/contracts/L1/rollup/iOVM_CanonicalTransactionChain.sol

@@ -18,11 +18,11 @@ interface iOVM_CanonicalTransactionChain {
      **********/
 
     event TransactionEnqueued(
-        address _l1TxOrigin,
-        address _target,
+        address indexed _l1TxOrigin,
+        address indexed _target,
         uint256 _gasLimit,
         bytes _data,
-        uint256 _queueIndex,
+        uint256 indexed _queueIndex,
         uint256 _timestamp
     );
 

packages/contracts/contracts/L2/messaging/OVM_L2CrossDomainMessenger.sol

@@ -102,7 +102,7 @@ contract OVM_L2CrossDomainMessenger is
         sentMessages[keccak256(xDomainCalldata)] = true;
 
         _sendXDomainMessage(xDomainCalldata, _gasLimit);
-        emit SentMessage(xDomainCalldata);
+        emit SentMessage(_target, _message, messageNonce, _gasLimit);
     }
 
     /**

packages/contracts/contracts/libraries/bridge/iOVM_CrossDomainMessenger.sol

@@ -11,9 +11,9 @@ interface iOVM_CrossDomainMessenger {
      * Events *
      **********/
 
-    event SentMessage(bytes message);
-    event RelayedMessage(bytes32 msgHash);
-    event FailedRelayedMessage(bytes32 msgHash);
+    event SentMessage(address indexed target, bytes message, uint256 messageNonce, uint256 gasLimit);
+    event RelayedMessage(bytes32 indexed msgHash);
+    event FailedRelayedMessage(bytes32 indexed msgHash);
 
 
     /*************

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

@@ -10,7 +10,7 @@ contract MockL2CrossDomainMessenger {
         uint256 messageNonce;
     }
 
-    event SentMessage(bytes message);
+    event SentMessage(address indexed target, bytes message, uint256 messageNonce, uint256 gasLimit);
 
     function emitSentMessageEvent(
         MessageData memory _message
@@ -18,13 +18,10 @@ contract MockL2CrossDomainMessenger {
         public
     {
         emit SentMessage(
-            abi.encodeWithSignature(
-                "relayMessage(address,address,bytes,uint256)",
             _message.target,
-                _message.sender,
             _message.message,
-                _message.messageNonce
-            )
+            _message.messageNonce,
+            0
         );
     }