Implement a ReturningIdGenerator that leverage `INSERT INTO .... RETURNING id`

[allan-simon]

Feature Request

Q	A
New Feature	yes
RFC	yes/no
BC Break	no

Summary

Add in AbstractIdGenerator a method

isInsertReturningGenerator() 

which will return false by default

Note: a "cleaner" way would have been to replace isPostInsertGenerator by a "getGeneratorKind" that return an enum pre/during/post but that would break BC

create a ReturningIdGenerator (I'm bad at naming) that will have function isInsertReturningGenerator { return true;}

so that after in BasicEntityPersister can be modified to have getInsertSQL to add a RETURNING %idColumn

and then in executeInserts we can do

$generatedId $stmt->executeQuery()->fetchOne;

that will divide by two the number of request required when doing inserts (as you will not need the pre or post insert request to get the id )

especially as this keyword is supported by several vendors (potgresql , mariadb , oracle among others ) and it will be opt-in for the user.

If that seems like a good idea I may work on a PR