This is based on a prototype by
Thirunarayanan Balathandayuthapani <thiru@mariadb.com>.

Binlog and Galera write-set replication information was written into
TRX_SYS page on each commit. Instead of writing to the TRX_SYS during
normal operation, InnoDB can make use of rollback segment header pages,
which are already being written to during a commit.

The following list of fields in rollback segment header page are added:
    TRX_RSEG_BINLOG_OFFSET
    TRX_RSEG_BINLOG_NAME (NUL-terminated; empty name = not present)
    TRX_RSEG_WSREP_XID_FORMAT (0=not present; 1=present)
    TRX_RSEG_WSREP_XID_GTRID
    TRX_RSEG_WSREP_XID_BQUAL
    TRX_RSEG_WSREP_XID_DATA

trx_sys_t: Introduce the fields
recovered_binlog_filename, recovered_binlog_offset, recovered_wsrep_xid.

To facilitate upgrade from older mysql or mariaDB versions, we will read
the information in TRX_SYS page. It will be overridden by the
information that we find in rollback segment header pages.

Mariabackup --prepare will read the metadata from the rollback
segment header pages via trx_rseg_array_init(). It will still
not read any undo log pages or recover any transactions.