xreplication: recovery mixed transacrtions

See the docbot request for details.

Closes #7932

@TarantoolBot document
Title: correct recovery of mixed transactions

In this patch implemented correct recovery of mixed transactions. To do
this, set  `box.cfg.force_recovery` to `true`. If you need to revert to
the old behavior, don't set the `force_recovery` option.

What to do when one node feeds the other a xlog with mixed transactions?
Let there be two nodes (`node#1` and `node#2`). And let the data be
replicated from `node#1` to `node#2`. Suppose that at some point in time,
`node#1` is restoring data from an xlog containing mixed transactions. To
replicate data from `node#1` to `node#2`, do the following:
1. Stop `node#2` and delete all xlog files from it
2. Restart `node#1` by setting `force_recovery` to `true`
3. Make `node#2` rejoin to `node#1` again.

(cherry picked from commit 2b1c8713)