What evolved to produce sweetness, plants or consumers?
None of the above.

Seeking sugar evolved long before animals, before multicellular organisms even.
Plant evolved a strategy to exploit it much much later with the evolution of fruit and nectar.  

Animals evolved to like the taste of sugar since it is the primary fuel almost all life metabolizes to live in an easy to digest form, literally a simple carbohydrate. plants use sugar substances as lures becasue that's what animals already wanted and plants were already making it. Also a lure is not going to evolve before the seeking behavior that would actually make it a lure. fruit and nectar are new sugar is one of the oldest metabolic compounds in existence. 

Metabolizing glucose is one of the shared characteristics between Eukaryotes and Bacteria and is present in nearly all life,source. Meaning it is was likely present in their common ancestor. This means plants and animals have been eating sugars since before they diverged into plants and animals. . Chemotaxis  of motile bacteria towards glucose is well understood, and likely predates the existence of eukaryotes. source

The production of sugar by photosynthetic bacteria predates the merging of Eukaryotic cells and chloroplast ancestors. It was present in the Cyanobacteria that gave rise to chloroplasts, meaning sugars were produced long before plants existed. source the attractive aspect was only exploited later with evolution of nectar and fruit.