Fixed #26682 -- Added support for Oracle identity columns.

Thanks Shai Berger and Tim Graham for reviews.

docs/releases/2.0.txt

@@ -206,6 +206,11 @@ Models
 * The new :class:`~django.db.models.functions.StrIndex` database function
   finds the starting index of a string inside another string.
 
+* On Oracle, ``AutoField`` and ``BigAutoField`` are now created as `identity
+  columns`_.
+
+  .. _`identity columns`: https://docs.oracle.com/database/121/DRDAA/migr_tools_feat.htm#DRDAA109
+
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