Pass conformance tests

[lifthrasiir]

libjxl has a battery of conformance tests, which is expected to become ISO/IEC 18181-3 in the future. They are coarser-grained tests and not suitable for detailed testing or estimating the actual progress, but they represent a good milestone so will be tracked here.

• [ ] alpha_nonpremultiplied
• [ ] alpha_premultiplied
• [x] alpha_triangle
• [ ] animation_icos4D
• [ ] animation_newtons_cradle
• [ ] animation_spline
• [ ] bench_oriented_BRG
• [ ] bicycles
• [ ] bike
• [ ] blendmodes
• [ ] cafe
• [ ] cmyk_layers
• [ ] delta_palette
  • Decodes but incorrect
• [ ] grayscale
  • Fails before TODO is reached
• [ ] grayscale_jpeg
  • Fails before TODO is reached
• [ ] grayscale_public_university
• [ ] lossless_pfm
• [ ] lz77_flower
  • Decodes and almost correct but has a subtle intensity difference
• [ ] noise
• [ ] opsin_inverse
  • Decodes but incorrect
• [ ] patches
• [ ] patches_lossless
• [ ] progressive
• [ ] spot
• [ ] sunset_logo
• [ ] upsampling