db: fix merge_cells using wrong column_definition
db: fix merge_cells using wrong column_definition

merge_cells() always used the regular column_definition, even when called
for a static row.

Fix by parametrizing it with a method to get the column_definition.

scylladb/scylla,kangkot/scylla,guiquanz/scylla,capturePointer/scylla,acbellini/scylla,rluta/scylla,stamhe/scylla,shaunstanislaus/scylla,eklitzke/scylla,dwdm/scylla,stamhe/scylla,acbellini/scylla,rentongzhang/scylla,wildinto/scylla,glommer/scylla,shaunstanislaus/scylla,bowlofstew/scylla,tempbottle/scylla,phonkee/scylla,linearregression/scylla,scylladb/scylla,raphaelsc/scylla,aruanruan/scylla,avikivity/scylla,gwicke/scylla,aruanruan/scylla,bowlofstew/scylla,kjniemi/scylla,glommer/scylla,justintung/scylla,guiquanz/scylla,rentongzhang/scylla,kjniemi/scylla,respu/scylla,dwdm/scylla,asias/scylla,eklitzke/scylla,kangkot/scylla,raphaelsc/scylla,justintung/scylla,asias/scylla,kangkot/scylla,dwdm/scylla,avikivity/scylla,guiquanz/scylla,avikivity/scylla,tempbottle/scylla,shaunstanislaus/scylla,respu/scylla,respu/scylla,justintung/scylla,scylladb/scylla,senseb/scylla,phonkee/scylla,kjniemi/scylla,bowlofstew/scylla,senseb/scylla,eklitzke/scylla,gwicke/scylla,senseb/scylla,stamhe/scylla,duarten/scylla,rluta/scylla,linearregression/scylla,tempbottle/scylla,phonkee/scylla,linearregression/scylla,wildinto/scylla,scylladb/scylla,capturePointer/scylla,asias/scylla,glommer/scylla,victorbriz/scylla,victorbriz/scylla,rluta/scylla,raphaelsc/scylla,capturePointer/scylla,gwicke/scylla,victorbriz/scylla,duarten/scylla,aruanruan/scylla,acbellini/scylla,rentongzhang/scylla,wildinto/scylla,duarten/scylla