Image grids at the codec level

[farindk]

Some codecs support images composed of tiles at the codec level (ISO 23001-17, h.265). Is there any use-case to support this for writing and fast access or would it be easier to just use the HEIF tiling mechanism and consider each coded image as a unit?

Note: clearly, we should support tiles in the codec when reading the image. The question is only whether we should provide some means to control the tiling at the codec level when writing the image and whether we should provide some means to decode these images only partially.

#1180