Add functionStaticCall and functionDelegateCall methods to Address library (#2333)

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

contracts/mocks/CallReceiverMock.sol

@@ -3,6 +3,7 @@
 pragma solidity ^0.6.0;
 
 contract CallReceiverMock {
+    string public sharedAnswer;
 
     event MockFunctionCalled();
 
@@ -20,6 +21,10 @@ contract CallReceiverMock {
         return "0x1234";
     }
 
+    function mockStaticFunction() public pure returns (string memory) {
+        return "0x1234";
+    }
+
     function mockFunctionRevertsNoReason() public payable {
         revert();
     }
@@ -37,4 +42,9 @@ contract CallReceiverMock {
             _array.push(i);
         }
     }
+
+    function mockFunctionWritesStorage() public returns (string memory) {
+        sharedAnswer = "42";
+        return "0x1234";
+    }
 }