Fixed #23957 -- Started deprecation toward requiring session verification.

Thanks Carl Meyer for review.
Fixed #23955 -- Corrected formset fields in topic guide.
Corrected example in Form.has_changed() docs.
Refs #23947 -- Made a modeladmin test cleanup after itself.
Fixed documentation of GeoModelAdmin.openlayers_url
Fixed #20968 -- Checked Spatialite metadata before migrations

Thanks Kenial S. Lee for the initial patch.
Ran 'CREATE EXTENSION postgis' during prepare_database hook

DatabaseWrapper.prepare_database has been introduced in 307de67073.