fix(document): make sure depopulate does not convert hydrated arrays to vanilla arrays

[vkarpov15]

Summary

One issue that popped up while I was working on #1635 is that depopulate() converts Mongoose arrays to vanilla JavaScript arrays. So band.depopulate('members'); band.members.addToSet(id); will error out because band.members is no longer a Mongoose array.

The approach I came up with is to use getValue(): if getValue() returns a Mongoose array, then we just modify the array in-place to avoid triggering setters. If not a Mongoose array, then we have a case where mpath is returning an array of values underneath a document array, like in the #10592 test case doc.depopulate('docArr.members'), so we fall back to setValue().

I left assert.ok(!band.embeddedMembers[0].$populated('member')); commented out because that assertion fails, but I want to look at it some more when we come back to #1635.

Examples

[hasezoey]

I left assert.ok(!band.embeddedMembers[0].$populated('member')); commented out because that assertion fails, but I want to look at it some more when we come back to #1635.

was this working before the PR?

[vkarpov15]

I confirmed this assertion fails before this PR. We will need to do some extra work to make sure depopulate() also updates subdocs' $populated().