Otherwise known as the much simpler alternative to joomla-framework/database#112

Our PostgreSQL support uses the native ext/pgsql PHP extension versus the PDO library support. The native extension forces us to add extra complexity to our API (i.e. for prepared statement support it mandates an extra parsing middleware). In the context of Joomla, PostgreSQL support is an extreme niche use case, with less than 0.1% of sites reporting stats in the last 90 days reporting using PostgreSQL as their driver, so devoting resources to this niche use case doesn't make much sense.

We can get consistent prepared statement support by switching the PostgreSQL support in the CMS to require PDO only and drop the native extension driver from our API. The PDO variant of the driver already exists in the Framework (and inherently 4.0). My proposal:

• In 3.9 and next minor Framework Database package release deprecate the ext/pgsql driver support
• In 3.9 backport the PDO PostgreSQL driver from the Framework to CMS (not required but it lets sites running PostgreSQL update their server configuration before attempting a 4.0 upgrade so it's one less thing that has to be changed during the upgrade)
• In Framework 2.0 Database package remove the ext/pgsql driver support