[1.7.x] Replaced input by textarea in forms docs

Backport of 5066fda34d from master.
[1.7.x] Fixed #23415 -- Added fields for unmanaged and proxy model migrations.

Thanks sky-chen for the report.

Backport of 215aa4f53b from master
[1.7.x] Fixed #23538 -- Added SchemaEditor for MySQL GIS.

Thanks Claude Paroz for suggestions and review.

Backport of 74e7f91e6d from master
[1.7.x] Fixed #23455 -- Forced related_name to be a unicode string during deconstruction.

Backport of 45bd7b3bd9 from master
[1.7.x] Added missing import removed in bad merge.