Split Proposal interface into two parts

[mossid]

Summary

type TextProposal in gov consists of two parts:

1. Data that can be customized by the external party, Title, Description and ProposalType
2. Data used internally by gov logic, all the other fields

In prior to apply #3565, we have to split the current interface to move minimal parts without moving definitions related to the internal logic. It is not safe to let the third party modules to implement the method related to internal logic, such as GetDepositEndTime() and GetTotalDeposit(), as it can return arbitrary value to skip(or somehow manipulate) the governance process. Those fields should be accessible only by the governance module.

Implementation

type ProposalProcess struct is replacing current type Proposal interface, as it is now stored in the state while the proposal is processed.

type ProposalProcess struct {
    Proposal Proposal
    ProposalID uint64
    Status ProposalStatus
    FinalTallyResult TallyResult
    //...
}

type Proposal interface is the part which the other custom proposal type can implement, and will be moved into types/

type Proposal interface {
    GetTitle() string
    GetDescription() string
    ProposalType() ProposalKind
    String() string
}

New method SubmitProposal is introduced where the other modules can call to submit a new proposal. When it is called, the keeper internally wraps it with ProposalProcess, thus no access to the internal parameters from the other modules.

func (k Keeper) SubmitProposal(ctx sdk.Context, proposal Proposal) error {}

[alexanderbez]

At a high level, this looks reasonable to me. Thanks @mossid