vote-interface: rename VoteState to VoteStateV3

[buffalojoec]

In preparation for introducing a new vote state (v4), this PR renames vote_state_v3::VoteState to vote_state_v3::VoteStateV3.

Normally, the module path could serve as the differentiator (ie. vote_state_v3::VoteState and vote_state_v3::VoteState), but that's brittle and we re-exported VoteState.

@joncinque I wanted to get your opinion on how best to handle this breaking change, as well as subsequent breaking changes to VoteStateVersions. We could introduce this change here as a minor release, where we mark the previous re-export as deprecated:

#[deprecated(..)]
pub use vote_state_v3::VoteStateV3 as VoteState;
pub use vote_state_v3::VoteStateV3;

However, since we plan to nuke VoteStateVersions, I wonder if the whole thing is ok to do in a major.

See #206

[joncinque]

Having done both in the past:

• StakeStateV2 https://github.com/solana-program/stake/blob/330d89c6246ab3fd35d02803386fa700be0455d6/interface/src/state.rs#L152
• v1 borsh module https://github.com/anza-xyz/solana-sdk/blob/master/borsh/src/v1.rs

I think both are fine approaches, but as you point out, the bigger issue is the re-export of VoteState in state/mod.rs.

It would be good to first do the rename + re-export change as you suggested, backport to the v2.x branch, and then remove VoteState in master for the next breaking release.

I don't see how VoteStateVersions fits into the rename here, but it doesn't seem too important for this PR. Is that correct?

[buffalojoec]

I don't see how VoteStateVersions fits into the rename here, but it doesn't seem too important for this PR. Is that correct?

I was alluding to the fact that everything we do to VoteStateVersions is also going to be a breaking change. So, I was wondering if it wasn't totally insane to just do all of the breakage in one major. There's not really a good deprecation strategy for adding a new variant to VoteStateVersions.

However, since the first change in Agave and likely most annoying breakage for everyone downstream is this rename, I agree with your points above.

[joncinque]

Ah gotcha, yeah we can certainly remove VoteStateVersions in the next major release!

We should just deprecate it first, similar to what this PR is doing.