map of Tuple and NamedTuple should return a Tuple or NamedTuple

[rafaqz]

Array is a strange return type for this interaction:

julia> map(+, (1, 2), (x=1, y=2))
2-element Array{Int64,1}:
 2
 4

Suddenly we have an allocating (and potentially unstable) type with different properties to a tuple. This produces undexpected and hard to find bugs.

The path of least surprise when using map on two objects with Tuple in their name would be to return some kind of Tuple.

Obviously this is a breaking change, so this is for 2.0.

[ederag]

Related, interesting discussion: #5794