Added migration for site test app depending on contrib.sites
Replaced DatabaseCreation sql methods by schema editor equivalents

Also used schema editor in migrate to sync unmigrated apps (sync_apps).
Refs #22340. Thanks Tim Graham for the review.
Removed models.Field.bind() -- unused/undocumented since at least 1.0.
Fixed #24037 -- Prevented data loss possibility when changing Meta.managed.

The migrations autodetector now issues AlterModelOptions operations for
Meta.managed changes instead of DeleteModel + CreateModel.

Thanks iambibhas for the report and Simon and Markus for review.