copy of https://github.com/mariadb-corporation/mariadb-columnstore-engine/pull/3021
Propagate the TL lock to TL_READ_NO_INSERT, blocking any concurrent writes until the end of a copy stage.
After that, this lock will be unlocked, allowing a window to write into a table before MDL is upgraded to exclusive (see online_alter_read_from_binlog call and the "alter_table_online_before_lock" debug syncpoint). This window will be covered by the second replication iteration after the lock upgrade
b9064ca925