Support `EXPLAIN EXTENDED`

[knutwannheden]

For some reason IntelliJ IDEA's "explain plan" functionality issues EXPLAIN EXTENDED statements, even though that EXTENDED keyword isn't documented as being part of the syntax: https://dev.mysql.com/doc/refman/8.0/en/explain.html. I suppose IntelliJ must be thinking it is MySQL 5.7, which is aware of that keyword: https://dev.mysql.com/doc/refman/5.7/en/explain.html

I am unsure what Dolt should about this, but it would be nice, if IntelliJ's own functionality can be used rather than manually having to prepend the query with EXPLAIN.

[jycor]

Fix for this is merged to main, and will be in next release (probably sometime next week).