Summary: These will, eventually, need to be moved to the new bridge and so must become standalone things. For *NativeArray, this is almost just moving them out into their own .h/.cpp files. The *NativeMaps are updated to be hybrids instead of countables (in addition to getting their own .h/.cpp).
Reviewed By: mhorowitz
Differential Revision: D3325169
fbshipit-source-id: 40cfcab92b3fb2310bcd4de8f39e82f85d404abd