wip: openjph HT decoder

[bradh]

This is a mostly-complete version of the OpenJPH JPEG-2000 + HT decoder.

To sort out the component to channel mapping, we need to pass down information from the j2kH item property. Is the best (only?) way to do make a C structure on the libheif side and push it down to the decoder plugin (via push_data())?

[farindk]

To sort out the component to channel mapping, we need to pass down information from the j2kH item property. Is the best (only?) way to do make a C structure on the libheif side and push it down to the decoder plugin (via push_data())?

The best way is probably to extend the plugin API with a J2K specific decoding function or a function to set the mapping.
Probably it will look something like this:

void (*set_jpeg2000_channel_mapping)(void* decoder, const int* channel, const int* component, int nComponents);

I don't know what is needed specifically, please specify as needed.