feat: Add a test to simplify deploy script testing (#12235)

* feat: Add a test to simplify deploy script testing

* fix: lint

* feat: Add clarifying comments to DeployVariations_Test

packages/contracts-bedrock/test/setup/DeployVariations.sol

+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.15;
+
+// Testing utilities
+import { CommonTest } from "test/setup/CommonTest.sol";
+import { ERC20 } from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+
+contract DeployVariations_Test is CommonTest {
+    function setUp() public override {
+        // Prevent calling the base CommonTest.setUp() function, as we will run it within the test functions
+        // after setting the feature flags
+    }
+
+    // Enable features which should be possible to enable or disable regardless of other options.
+    function enableAddOns(bool _enableCGT, bool _enableAltDa) public {
+        if (_enableCGT) {
+            ERC20 token = new ERC20("Silly", "SIL");
+            super.enableCustomGasToken(address(token));
+        }
+        if (_enableAltDa) {
+            super.enableAltDA();
+        }
+    }
+
+    /// @dev It should be possible to enable Fault Proofs with any mix of CGT and Alt-DA.
+    function testFuzz_enableFaultProofs(bool _enableCGT, bool _enableAltDa) public virtual {
+        enableAddOns(_enableCGT, _enableAltDa);
+        super.enableFaultProofs();
+        super.setUp();
+    }
+
+    /// @dev It should be possible to enable Fault Proofs and Interop with any mix of CGT and Alt-DA.
+    function test_enableInteropAndFaultProofs(bool _enableCGT, bool _enableAltDa) public virtual {
+        enableAddOns(_enableCGT, _enableAltDa);
+        super.enableInterop();
+        super.enableFaultProofs();
+        super.setUp();
+    }
+}