Sync with the latest releases of Galera

Currently, MariaDB uses an outdated version of the Galera subsystem, which contains many bugs that have already been found and fixed in other releases. Some of these bugs are fixed in the official release from Codership, but there are a lot of fixes that were made by the Percona team. In particular, we can talk about bugs and improvements like repoted as PXC#329, PXC#473, PXC#516, PXC#422, PXC# 23, PXC#445 and many others. Some of these bugs can cause interference with the code to speed up commit monitors within the MDEV-15423 task. To make MariaDB more stable and free from the Galera's bugs already known by other releases, and to make debugging of the MDEV-15423 code easier and to combine all three main Galera releases, maybe we should port all progressive changes from the current releases of the Galera (from Codership and/or from PXC) into the MariaDB's Galera repository.