Thanks to Reto Aebersold for reporting the issue and Tim Graham and
Claude Paroz for the review.

Changed squashmigrations to not instantiate a MigrationExecutor,
but to directly use a MigrationLoader instance instead.

I changed "appears" to "appear" and emphasized the word "not" to match
the rest of the document.

The locale code can contain a variant after @, so allowed that.

Thanks Carl Meyer for review.

Thanks datakid for the report

Refs #15053.

This now works for multiple Django engines and recursive loaders.
Support for non-Django engines is still pending.

Refs #15053.

Thanks Simon Charette and Tim Graham for the reviews.

Thanks Serhiy Zahoriya for the suggestion and Tim Graham for the
review.

Thanks tttomekkk for the report.

Refs #24354 -- Prevented repointing of relations on superclasses when migrating a subclass's name change

The issue was hidden on 1.8+ until #24573 due to a bug inside the model
reloading process.

Forwardport of patch from ae87ad00

Changed ModelState.clone() to create a shallow copy of self.fields
and self.managers.