Generalise two approaches for storing set/map values

[medikoo]

There are two ways:

1. Store each key/value (in case of map), or each item (in case of set) via separate record
2. Store full set or map result with one record.

Currently (1) is used for directly operated (not computed) sets and maps, and (2) is used for computed sets.
It'll be great to have an option to use both (1) and (2) for direct and computed data handling in both map and set cases.