Add Governor module for governance-settable parameters (#2904)

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

contracts/mocks/GovernorTimelockControlMock.sol

@@ -3,13 +3,16 @@
 pragma solidity ^0.8.0;
 
 import "../governance/extensions/GovernorTimelockControl.sol";
+import "../governance/extensions/GovernorSettings.sol";
 import "../governance/extensions/GovernorCountingSimple.sol";
 import "../governance/extensions/GovernorVotesQuorumFraction.sol";
 
-contract GovernorTimelockControlMock is GovernorTimelockControl, GovernorVotesQuorumFraction, GovernorCountingSimple {
-    uint256 immutable _votingDelay;
-    uint256 immutable _votingPeriod;
-
+contract GovernorTimelockControlMock is
+    GovernorSettings,
+    GovernorTimelockControl,
+    GovernorVotesQuorumFraction,
+    GovernorCountingSimple
+{
     constructor(
         string memory name_,
         ERC20Votes token_,
@@ -20,12 +23,10 @@ contract GovernorTimelockControlMock is GovernorTimelockControl, GovernorVotesQu
     )
         Governor(name_)
         GovernorTimelockControl(timelock_)
+        GovernorSettings(votingDelay_, votingPeriod_, 0)
         GovernorVotes(token_)
         GovernorVotesQuorumFraction(quorumNumerator_)
-    {
-        _votingDelay = votingDelay_;
-        _votingPeriod = votingPeriod_;
-    }
+    {}
 
     function supportsInterface(bytes4 interfaceId)
         public
@@ -37,14 +38,6 @@ contract GovernorTimelockControlMock is GovernorTimelockControl, GovernorVotesQu
         return super.supportsInterface(interfaceId);
     }
 
-    function votingDelay() public view override returns (uint256) {
-        return _votingDelay;
-    }
-
-    function votingPeriod() public view override returns (uint256) {
-        return _votingPeriod;
-    }
-
     function quorum(uint256 blockNumber)
         public
         view
@@ -76,6 +69,10 @@ contract GovernorTimelockControlMock is GovernorTimelockControl, GovernorVotesQu
         return super.state(proposalId);
     }
 
+    function proposalThreshold() public view override(Governor, GovernorSettings) returns (uint256) {
+        return super.proposalThreshold();
+    }
+
     function _execute(
         uint256 proposalId,
         address[] memory targets,