Update initializer modifier to prevent reentrancy during initialization (#3006)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
(cherry picked from commit 08840b9f8c)

contracts/mocks/InitializableMock.sol

@@ -10,16 +10,25 @@ import "../proxy/utils/Initializable.sol";
  */
 contract InitializableMock is Initializable {
     bool public initializerRan;
+    bool public onlyInitializingRan;
     uint256 public x;
 
     function initialize() public initializer {
         initializerRan = true;
     }
 
-    function initializeNested() public initializer {
+    function initializeOnlyInitializing() public onlyInitializing {
+        onlyInitializingRan = true;
+    }
+
+    function initializerNested() public initializer {
         initialize();
     }
 
+    function onlyInitializingNested() public initializer {
+        initializeOnlyInitializing();
+    }
+
     function initializeWithX(uint256 _x) public payable initializer {
         x = _x;
     }
@@ -32,3 +41,21 @@ contract InitializableMock is Initializable {
         require(false, "InitializableMock forced failure");
     }
 }
+
+contract ConstructorInitializableMock is Initializable {
+    bool public initializerRan;
+    bool public onlyInitializingRan;
+
+    constructor() initializer {
+        initialize();
+        initializeOnlyInitializing();
+    }
+
+    function initialize() public initializer {
+        initializerRan = true;
+    }
+
+    function initializeOnlyInitializing() public onlyInitializing {
+        onlyInitializingRan = true;
+    }
+}