Remove duplication between 'alter column' sub-operations. Pull:
column duplication and trigger creation on migration start
column rename and trigger removal on complete
trigger and column drop on rollback
up to the parent 'alter column' operation. This removes a lot of duplicated code from the sub-operations and will make it easier to support multiple sub-operations in one 'alter column' operation.
Remove duplication between 'alter column' sub-operations. Pull:
up to the parent 'alter column' operation. This removes a lot of duplicated code from the sub-operations and will make it easier to support multiple sub-operations in one 'alter column' operation.
Part of #336