feat(FDL_postmigr_3.2.12): Coalesce alterations of multiple columns (refs #5190)

Optimize table alteration by altering all the columns in a single pass
instead of multiples passes.
Merge pull request #1358 from eguaj/3.2-A5190

feat(FDL_postmigr_3.2.12): Coalesce alterations of multiple columns (closes #5190)