Fixed #22826 -- Improved internal usage of Query.setup_joins.
Removed unnecessary attribute assigment to SQLCompiler.
Improved code style of Query.table_alias() usage.
Merge pull request #2806 from jorgecarleitao/issue22826

Fixed #22826 -- Improved internal usage of Query.setup_joins.
Fixed #22842
Merge pull request #2810 from magrinidiego/ticket_22842_tutorial_test

Fixed #22842
Improve error message for missing migrations in an app
Fixed #22563: Added migration to admin, fixed a few more loader issues.
Fixed #22660: Doc'd you can't have unmigrated apps depend on migrated
Fixed #22833: Autodetector not doing through mapping correctly
Persist non-schema-relevant Meta changes in migrations
Fixed #22470: Full migration support for order_with_respect_to
Fixed #22568: Better proxy model support in migrations
Added database migration for contrib.sites.

refs #22170.
Added database migration for contrib.flatpages.

refs #22170.
Added database migration for contrib.redirects.

refs #22170.
Fixed several flake8 errors
Fixed #22844: Duplicate SQL for SQLite FKs
Removed usaged of contrib.sessions as a placeholder in migration tests.

Without this, we're unable to add actual migrations for the app.
Added database migration for contrib.sessions.

refs #22170.