DDC-2875: [GH-890] [DBAL-563] Add general IDENTITY generator type support for sequence emulating platforms

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of deeky666:

Url: #890

Message:

This is a follow-up PR for doctrine/dbal#428 as discussed in [DBAL-563](http://www.doctrine-project.org/jira/browse/[DBAL-563]%28http://www.doctrine-project.org/jira/browse/DBAL-563%29) which adds IDENTITY generator type support for platforms that do not natively support identity columns but can emulate them via sequences.
This replaces the current workaround for PostgreSQL SERIAL columns in favour of a more general approach. With this patch now IDENTITY generator can also be used with Oracle which did not work before. Future platforms can also make use of this approach if necessary.

[doctrinebot]

• relates to DBAL-563: Oracle "IDENTITY" last inserted ID is returning 0 instead of the real ID

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-890] was closed:
#890

[doctrinebot]

Issue was closed with resolution "Fixed"