…nged` while rollback at a special height (#2136)

closes: #2137 #1074

## Description
Rollback at a specific height causes the node to fail to start. This is
caused by the error code:

https://github.com/cometbft/cometbft/blob/635d0b596c7300c98caa57e7aab26a7a4579ab97/internal/state/rollback.go#L71

According to the definition of the `State` struct as below

https://github.com/cometbft/cometbft/blob/635d0b596c7300c98caa57e7aab26a7a4579ab97/internal/state/state.go#L63
`LastHeightValidatorsChanged` satisfy the following condition under any
circumstances
1 <= `state.LastHeightValidatorsChanged` <= `state.LastBlockHeight + 1 +
1`

this condition can also be confirmed by looking at the code in `func
(store dbStore) save(state State, key []byte) error`

https://github.com/cometbft/cometbft/blob/635d0b596c7300c98caa57e7aab26a7a4579ab97/internal/state/store.go#L229

`state.LastHeightValidatorsChanged` is with `nextHeight +
1`(`state.LastBlockHeight + 1 + 1`) corresponds.

When we rollback from block height `state.LastHeightValidatorsChanged -
1` to height `state.LastHeightValidatorsChanged - 2`,
`newState.LastHeightValidatorsChanged` would be wrong to modified into
the `state.LastHeightValidatorsChanged - 1`

## Issue
Let me give an example to describe the issue:

### example
> ... => [block 242 (5validators)] ==state1(5validators)==> [block 243
(5validators)] ==state2(4validators)==> [block 244 (4validators)] => ...

1. Assume that the current height of the block is 243, current state is
`state2` and `state2.LastHeightValidatorsChanged` == 244, validatorSet
changed to 4 validators in the block 244 and state2

2. Rollback to block 242 and state1, the target `rollbackHeight` == 242

3. Since the error code,
https://github.com/cometbft/cometbft/blob/635d0b596c7300c98caa57e7aab26a7a4579ab97/internal/state/rollback.go#L71
`state1.LastHeightValidatorsChanged` was changed to 243 incorrectly and
it should be 244

4. After rollbacked to block 242, node could not start properly

## Solution
See code for details.

#### PR checklist

- [x] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [x] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [x] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec

Co-authored-by: Andy Nogueira <me@andynogueira.dev>
Co-authored-by: Anton Kaliaev <anton.kalyaev@gmail.com>
(cherry picked from commit 269219c)