UPDATE elements of deeply nested arrays

N1QL provides the

UPDATE SET / UNSET ... FOR ...

syntax for updating nested array elements. However, this only supports one array level. We need to support additional array levels by chaining the FOR clauses. See user request at

https://forums.couchbase.com/t/how-to-add-new-field-to-each-element-of-array-which-is-inside-another-array/8509/5
http://stackoverflow.com/questions/37538047/n1ql-how-to-add-new-field-to-each-element-of-array-which-is-inside-another-arr/37546122#37546122