Fix behaviour of arrays with minItems and default

[spacebaboon]

When providing both default (as a list) and minItems to a field of type array
the defaults are treated as a single value that ends up in each field.

Relates to ticket
#631

Expected behavior

defaults should be treated as a list and be given one entry each, i.e.:

When minItems > default.length provide empty or item-level default fields after the fields with the default values.
When minItems <= default.length provide one field per value in default list.

Actual behavior

The default items gets mashed together into each field

Checklist

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