BF immunity of local sessions with wsrep_on = OFF

Local sessions having wsrep_on = OFF configuration and which conflict with applier executions may or may not be BF aborted depending on where the conflict happens:

• with MDL lock conflicts, the local session will be BF aborted
• with innodb lock conflict, the local session will not be aborted

This split behavior is probably due to regression introduced by fix for MDEV-34836: (TOI on parent table must BF abort SR in progress on a child), (commit 231900e5bb15e5d6d90b8a6daf38a0b21d1a19e7)
..having a new function for checking BF abortability:

static bool wsrep_will_BF_abort(const lock_t *lock, const trx_t *trx)

{

  ut_ad(wsrep_thd_is_BF(trx->mysql_thd, false));

  /* Don't BF abort system transactions. */

  if (!lock->trx->is_wsrep())

    return false;

...

Here, lock->trx->is_wsrep() returns 0 for local session with wsrep_on=OFF, and this avoids BF aborting. The comment says that only system threads were supposed to have immunity, but now also non wsrep local sessions got immunity as well.