Create properties of the governance system

[WhatisRT]

This is the companion to https://github.com/input-output-hk/cardano-ledger/issues/3149.

• [ ] #413
• [ ] #414
• [ ] #415
• [ ] #412
• [ ] #417

[WhatisRT]

Here are a few rewarding deposits:

• If a transaction contains k proposals, the deposit pot for governance actions grows by k * govDeposit
• For all proposal deposits d currently in a block, there exists an epoch e where if it contains a block, the deposit for d is not in the deposit pot anymore.
• For a stake address a and a transaction that spends an input with stake address a to propose something and returning the remainder back to a, otherwise not touching a, the voting power of a does not change.

[WhatisRT]

• EnactState only changes when governance actions are enacted

[WhatisRT]

• When a DRep votes, that vote always applies to the GA

[WhatisRT]

Not strictly related to governance, but:

• At the epoch boundary, dom DState.rewards is constant
• dom DState.rewards = DepositPurpose.CredentialDeposit^{-1} (dom UTxOState.deposits)