Pull Request for no issue.

Summary of Changes

This PR adds the "IF EXISTS" condition to all "CREATE TABLE" statements in any SQL scripts for Postgresql as supported since Postgresql version 9.1, so the Postgresql SQL scripts work in the same way as the SQL scripts for mysql.

See http://stackoverflow.com/questions/1766046/postgresql-create-table-if-not-exists and https://www.postgresql.org/docs/9.2/static/sql-createtable.html regarding the "CREATE TABLE IF EXISTS" support in Postgresql.

Following kinds of scripts are affected:

• Joomla installation script joomla.sql or Postgresql
• All present schema update SQL scripts for Postgresql
• All present special installation SQL scripts for Postgresql (currently only one for com_finder)

These 3 kinds of changes have been added with separate commits so they can be cherry-picked by a maintainer if this PR is not acceptable completely, e.g. in case PLT hates changes on old schema update SQL scripts.

The database schema manager's change item class for Postgresql already supports the "CREATE TABLE IF EXISTS" statements and so does not need to be changed, see https://github.com/joomla/joomla-cms/blob/4.0-dev/libraries/src/CMS/Schema/ChangeItem/PostgresqlChangeItem.php#L194

Testing Instructions

• Code review: Check e.g. with findstr on MS Windows or grep on Linux or in an editor with a search function that all "CREATE TABLE" statements in the changed files have been changed, no statement has been forgotten.
• New Joomla installation: All works like before, result is same as without this PR.
• Joomla Update: Works like before, result is same as without this PR.
• Database schema manager: Extensions -> Manage -> Database shows same results and same number of statements as without this PR.

Expected result

All works like before, result is same as without this PR.

Actual result

Same as expected result.

Documentation Changes Required

None.