BufferTile buffer preservation

[pomadchin]

With the focal operations support #563 and introduction of the BufferTile into GeoTrellis locationtech/geotrellis#3419 we got an extra Tile type (in addition to the RasterRef, Tile and ProjectedRasterTile). This extra type requires a proper handling not only in all focal functions, but also in local (after performing a local operation information about the Tile Buffer should be preserved).

It is possible to solve it via a smiliar pattern matching and "unpacking" of the BufferTile from the depth of RF structures, or via moving all internal RF operations to the BufferTile by default.

This task is the follow up issue of the (eventually) merged #563