Table names and database name now enclosed in backticks.
admin/cli/mysql_collation.php failed if $CFG->prefix was blank with
MySQL 8.0 because table 'groups' conflicted with a new reserved word.
Note that this quotes both mysql_collation.php and mysql_compressed_rows.php
but only the former was mal-functioning.
The case of mysql_compressed_rows.php is a little bit special because
not all tables are processed, only those having big rows. And the groups
table is not one of them. In any case, better add the quotes there for
any future case.
Also, when testing this patch https://tracker.moodle.org/browse/MDL-71512
was discovered and will need to be fixed to make core 100% compliant
with MySQL 8.0 and MariaDB 10.6 and up.
dirname() is a slow function compared with __DIR__ and using
'/../'. Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code. This allows those required includes to perform as
best as possible in this situation.
