Allow Governor + CompoundTimelock to manage native tokens (eth) in and out of the timelock contract. (#2849)

* Change GovernorTimelockCompound to support ETH in Timelock

* refactor compound timelock module

* Allow governor to receive ETH is executor == address(this)

contracts/governance/Governor.sol

@@ -55,6 +55,13 @@ abstract contract Governor is Context, ERC165, EIP712, IGovernor {
         _name = name_;
     }
 
+    /**
+     * @dev Function to receive ETH that will be handled by the governor (disabled if executor is a third party contract)
+     */
+    receive() external payable virtual {
+        require(_executor() == address(this));
+    }
+
     /**
      * @dev See {IERC165-supportsInterface}.
      */

contracts/governance/extensions/GovernorTimelockCompound.sol

@@ -177,8 +177,9 @@ abstract contract GovernorTimelockCompound is IGovernorTimelock, Governor {
     ) internal virtual override {
         uint256 eta = proposalEta(proposalId);
         require(eta > 0, "GovernorTimelockCompound: proposal not yet queued");
+        Address.sendValue(payable(_timelock), msg.value);
         for (uint256 i = 0; i < targets.length; ++i) {
-            _timelock.executeTransaction{value: values[i]}(targets[i], values[i], "", calldatas[i], eta);
+            _timelock.executeTransaction(targets[i], values[i], "", calldatas[i], eta);
         }
     }
 

contracts/mocks/GovernorCompMock.sol

@@ -20,8 +20,6 @@ contract GovernorCompMock is Governor, GovernorVotesComp, GovernorCountingSimple
         _votingPeriod = votingPeriod_;
     }
 
-    receive() external payable {}
-
     function votingDelay() public view override returns (uint256) {
         return _votingDelay;
     }

contracts/mocks/GovernorMock.sol

@@ -21,8 +21,6 @@ contract GovernorMock is Governor, GovernorVotesQuorumFraction, GovernorCounting
         _votingPeriod = votingPeriod_;
     }
 
-    receive() external payable {}
-
     function votingDelay() public view override returns (uint256) {
         return _votingDelay;
     }