Add string and bytes support to the StorageSlots library (#4008)

Co-authored-by: Francisco <frangio.1@gmail.com>

contracts/mocks/StorageSlotMock.sol

@@ -5,7 +5,7 @@ pragma solidity ^0.8.0;
 import "../utils/StorageSlot.sol";
 
 contract StorageSlotMock {
-    using StorageSlot for bytes32;
+    using StorageSlot for *;
 
     function setBoolean(bytes32 slot, bool value) public {
         slot.getBooleanSlot().value = value;
@@ -38,4 +38,40 @@ contract StorageSlotMock {
     function getUint256(bytes32 slot) public view returns (uint256) {
         return slot.getUint256Slot().value;
     }
+
+    mapping(uint256 => string) public stringMap;
+
+    function setString(bytes32 slot, string calldata value) public {
+        slot.getStringSlot().value = value;
+    }
+
+    function setStringStorage(uint256 key, string calldata value) public {
+        stringMap[key].getStringSlot().value = value;
+    }
+
+    function getString(bytes32 slot) public view returns (string memory) {
+        return slot.getStringSlot().value;
+    }
+
+    function getStringStorage(uint256 key) public view returns (string memory) {
+        return stringMap[key].getStringSlot().value;
+    }
+
+    mapping(uint256 => bytes) public bytesMap;
+
+    function setBytes(bytes32 slot, bytes calldata value) public {
+        slot.getBytesSlot().value = value;
+    }
+
+    function setBytesStorage(uint256 key, bytes calldata value) public {
+        bytesMap[key].getBytesSlot().value = value;
+    }
+
+    function getBytes(bytes32 slot) public view returns (bytes memory) {
+        return slot.getBytesSlot().value;
+    }
+
+    function getBytesStorage(uint256 key) public view returns (bytes memory) {
+        return bytesMap[key].getBytesSlot().value;
+    }
 }