Update ChangeDescription.fields_changed to support 4GB of data on MySQL.
Review Request #1499 — Created Dec. 14, 2018 and updated
The fields_changed field (Djblets's JSONField) was forcing the field type as "text" on MySQL, limiting the size to only 64K. Djblets has been updated to use the default "longtext", but this only helps on new databases. This new evolution alters MySQL databases to be "longtext," forever ending the field length/corruption issues. Fixes bug #1481