Fixed #23992 -- Optimized reorder_suite functions using OrderedSet
Fixed timesince translations for Korean

Refs #23989.
Forward port of eb632bfba from stable/1.7.x.
Merge pull request #3730 from tchaumeny/test_suite_reorder

Fixed #23992 -- Optimized reorder_suite functions using OrderedSet
Fixed #23991 -- Apparently, Oracle doesn't need the decimal field converter

Thanks Josh Smeaton for review.
Changed internal storing of abstract and concrete managers to be in a single list.

This commit prepares the internal manager layout to be serialized by
migrations; refs #23822.
Fixed #23822 -- Added support for serializing model managers in migration

Thanks to Shai Berger, Loïc Bistuer, Simon Charette, Andrew Godwin,
Tim Graham, Carl Meyer, and others for their review and input.
Fixed #23884 -- Moved FlatPageSitemap into django.contrib.flatpages.
Refs #23947 -- admin_views fix to PostgreSQL autoincrement behavior
Refs #23947 -- generic relations regress fix

Fix PostgreSQL id column auto increment behavior, where the id counter
is not restored to 0 after deleting objects.
Refs #23947 -- queries test fix

Specify the id to avoid pkey value conflict with objects created in
SetupTestData.
Refs #23947 -- migrations test operations fix

The test `test_alter_field_m2m` was trying to drop a table but it was
raising an exception telling that objects depend on that table. The
exception suggested to add CASCADE to drop the dependent objects too.

A new try/except was needed because just addind the cascade was
triggering some errors when running with sqlite database.