Focal operations on Tensors

[jpolchlo]

Rasterframes is still devoid of focal operations, but we frequently see use cases that require this capability. It is a difficult problem by virtue of needing to have a deep infrastructure. The minimal success conditions for this task require buffered tiles or tensors, a reading infrastructure where the buffer size can be communicated to the data source, modifications to the local op infrastructure to accept buffered inputs, and a new focal op infrastructure.

In my wildest dreams, this task would also provide a static optimizer to spark SQL logical plans which determines the buffer size from the tree of operations (but this has numerous complications).

I'm tagging this as an Epic, so that this larger task may be broken into narrower constituent tasks.

Requires #19

[echeipesh]

The focal ops are available via python