Add GPU and Dask support for Focal tools: mean, apply, hotspots (#238)

* refactor

* move kernel creation to convolution.py

* import fix

* convolve_2d: remove padding, remove use_cuda param

* convolve_2d: add cupy tests

* nan edge effect

* refactor

* kernel: add tests

* convolve_2d: dask numpy case

* convolve_2d: dask cupy case, raise not implemented

* convolution: test dask cupy not implemented

* focal mean: refactor

* focal mean: dask numpy case, nan edge effect

* focal mean: check if exclude nan

* focal mean: cupy case

* focal mean: dask cupy case not implemented

* focal apply: numpy case with test

* focal apply: dask numpy case

* focal apply: gpu cupy support

* focal hotspots: refactor

* focal hotspots: use raster.data for calculation

* focal hotspots: refactor

* focal hotspots: cupy case

* focal hotspots: dask numpy case

* focal hotspots: dask cupy case not implemented

* update readme

* flake8 fix

* flake8 fix

* hotspots: avoid early compute global_std

* correct typo

Author: thuydotm

README.md

@@ -93,10 +93,10 @@ In the GIS world, rasters are used for representing continuous phenomena (e.g. e
 
 | Name | NumPy xr.DataArray | Dask xr.DataArray | CuPy GPU xr.DataArray | Dask GPU xr.DataArray |
 |:----------:|:----------------------:|:--------------------:|:-------------------:|:------:|
-| [Apply](xrspatial/focal.py) | ✅️ |  |  |  |
-| [Hotspots](xrspatial/focal.py) | ✅️ | |  |  |
-| [Mean](xrspatial/focal.py) | ✅️ |  | | |
-| [Focal Statistics](xrspatial/focal.py) | ✅️ | | ✅️ | |
+| [Apply](xrspatial/focal.py) | ✅️ | ✅️ | ✅️ |  |
+| [Hotspots](xrspatial/focal.py) | ✅️ | ✅️ | ✅️ |  |
+| [Mean](xrspatial/focal.py) | ✅️ | ✅️ | ✅️ | |
+| [Focal Statistics](xrspatial/focal.py) | ✅️ | ✅️ | ✅️ | |
 
 -------