Construct NeighboringCellInfo from CellInfo

As part of removing neighboring cell info this
CL adds support for constructing a NeighboringCellInfo
object from a CellInfo object.

Bug: 62490173
Test: tested manually using SL4A with both O-MR1 and current
    target SDKs
Change-Id: I278487e506b07ab97589da85f69f1188c73b6eb9