contracts-bedrock: dispute game factory event

Adds an event that is emitted when a dispute game implementation
is added to the dispute game factory contract. This will make
it easier to track the state of the contract.

packages/contracts-bedrock/.gas-snapshot

@@ -29,7 +29,7 @@ DeployerWhitelist_Test:test_owner_succeeds() (gas: 7582)
 DeployerWhitelist_Test:test_storageSlots_succeeds() (gas: 33395)
 DisputeGameFactory_Test:test_owner_succeeds() (gas: 7582)
 DisputeGameFactory_Test:test_setImplementation_notOwner_reverts() (gas: 11191)
-DisputeGameFactory_Test:test_setImplementation_succeeds() (gas: 32635)
+DisputeGameFactory_Test:test_setImplementation_succeeds() (gas: 38528)
 DisputeGameFactory_Test:test_transferOwnership_notOwner_reverts() (gas: 10979)
 DisputeGameFactory_Test:test_transferOwnership_succeeds() (gas: 13180)
 FeeVault_Test:test_constructor_succeeds() (gas: 10736)

packages/contracts-bedrock/contracts/dispute/DisputeGameFactory.sol

@@ -113,6 +113,7 @@ contract DisputeGameFactory is Ownable, IDisputeGameFactory {
      */
     function setImplementation(GameType gameType, IDisputeGame impl) external onlyOwner {
         gameImpls[gameType] = impl;
+        emit ImplementationSet(address(impl), gameType);
     }
 
     /**

packages/contracts-bedrock/contracts/dispute/IDisputeGameFactory.sol

@@ -23,6 +23,13 @@ interface IDisputeGameFactory {
         Claim indexed rootClaim
     );
 
+    /**
+     * @notice Emitted when a new game implementation added to the factory
+     * @param gameType The type of the DisputeGame.
+     * @param impl The implementation contract for the given `GameType`.
+     */
+    event ImplementationSet(address impl, GameType gameType);
+
     /**
      * @notice `games` queries an internal a mapping that maps the hash of
      *         `gameType ++ rootClaim ++ extraData` to the deployed `DisputeGame` clone.

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

@@ -18,6 +18,8 @@ contract DisputeGameFactory_Test is Test {
         Claim indexed rootClaim
     );
 
+    event ImplementationSet(address impl, GameType gameType);
+
     function setUp() public {
         factory = new DisputeGameFactory(address(this));
         fakeClone = new FakeClone();
@@ -105,6 +107,9 @@ contract DisputeGameFactory_Test is Test {
         // There should be no implementation for the `GameType.FAULT` enum value, it has not been set.
         assertEq(address(factory.gameImpls(GameType.FAULT)), address(0));
 
+        vm.expectEmit(true, true, true, true, address(factory));
+        emit ImplementationSet(address(1), GameType.FAULT);
+
         // Set the implementation for the `GameType.FAULT` enum value.
         factory.setImplementation(GameType.FAULT, IDisputeGame(address(1)));