[SERVER-6436] Add method for unwinding nested arrays - MongoDB Jira

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Right now $unwind can only unwind an array that is not nested within another array. For example 'a.b' can be unwound in this document:

{ a:{ b:[ 1, 2 ] } }

but not in this one:

{ a:[ { b:1 }, { b:2 } ] }

and not in this one:

{ a:[ { b:[ 1, 2 ] } ] }

Current behavior is to not unwind anything in these cases.

is related to

SERVER-23754 $unwind should error when it encounters arrays within arrays

SERVER-40134 Distinct command against a view can return incorrect results when the distinct path is multikey

related to

SERVER-23754 $unwind should error when it encounters arrays within arrays