Improve YUV/RGB conversion handling

[maryla-uc]

Some matrix coeffcients values are currently unsupported and trying to use avifdec on an avif image that uses such a matrix coefficient to save it to jpg/png will result in a cryptic "Conversion to RGB failed" error.

Similarly, trying to encode an image with avifenc while setting --cicp to e.g. 1/13/10 (where 10 is the currently unsupported AVIF_MATRIX_COEFFICIENTS_BT2020_CL value) will result in the message Conversion to YUV failed

The tools should at the very least provide a more useful error, and ideally handle all possible matrix coefficient values.

See:

libavif/src/reformat.c

Line 108 in 3e4b9c8

// These matrix coefficients values are currently unsupported. Revise this list as more support is added.

See for example the test image Chimera_10bit_cropped_to_1920x1008_with_HDR_metadata.avif in AOMediaCodec/av1-avif#202