Add a new function to find the global work size given the output image and
the required block alignment, then use it in the overlay, program and unsharp
filters. Fixes the overlay and unsharp filters applying the kernel to
locations outside the frame when subsampled planes are present.
Intended to replace existing opencl mode of the unsharp filter.
Supports many more pixel formats and works without immediate upload
and download of frame data. The options are compatible with the
existing filter.
