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

[Amxx]

In GovernorBravo (and Alpha), the execute function must send the value attached to the proposal to the timelock

This means two things:

• The executor must give away all the Eth needed to run the proposal
• Any Eth present on the timelock cannot be moved away from it (such proposal would require the executor to provide an equal amount, resulting in a null result from the timelock point of view).

This means that governor + compound timelock cannot be used to manage big funds in Eth.

This PR moves away from compound behavior to enable such usecases.

Note: this issue does NOT affect OZ Governor + TimelockController combo

[tarrencev]

Thanks for helping look into this. I've confirmed that our integration test passes with this change.

[frangio]

I don't think this change is ideal because it is different from the behavior of GovernorBravo in an important way: ETH sent to the Governor will be locked in it. I think this is a more general problem we should tackle for ERC20 sent to the Governor as well, although that is not a new problem with respect to GovernorBravo. I would not merge this change as is without a way to retrieve those funds.

An alternative change is to send Math.min(this.balance, values[i]). I think this results in a way to execute proposals that can use both the funds in the Governor and in the Timelock.

[Amxx]

What about the difference of behavior between our governors depending on the timelock module used? To me they are more problematic.

Also, the governor should not have a receive function if there is a timelock module (or if there is one it should revert)

[frangio]

Looks good to me!

[frangio]

Looks good to me!