Construct: the order of Computed fields matter

[Mingun]

Currently some tests on https://ci.kaitai.io/ are failed because of that fact that instance fields are sorted alphabetically (due to SortedMap used for storage) and generated in the same order.

Sorting of instances are good thing which will ensure stable output friendly for diffs, but Construct currently cannot calculate dependents inside of Computed fields and raises an error instead.

Although problem seems to be resolved on Construct side, it also could be useful to generate Computed properties in a topological order of dependencies.