BibFormat: larger column `format.code`

* addresses (#2072)

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
`format_larger_values` name may be misleading, since one does not know which format value is getting larger.  Can you please rename to something like `format_code_larger` or even better `format_code_varchar20` for example?  This will better indicate that it is `format.code` column that is getting larger.