Fixed #20968 -- Checked Spatialite metadata before migrations

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

DatabaseWrapper.prepare_database has been introduced in 307de67073.
Fixed typo in spatialite.txt

Thanks Tim Graham for spotting the error.
Remove text-mangling of default values.
Fixed #23961 -- Clarified when makemigrations will create a directory.
Refs #23947 -- Prevented staticfiles tests from having side effects.
Fixed incorrect filter name in docs/topics/i18n/translation.txt.
Fixed #23956 -- Fixed migration creation for multiple table inheritance
Fixed typo in admin deprecation message.
Fixed #23977 -- Added setdefault() method to HttpResponse
Appeased spell checker.