[Enhancement] Use wuffs/fpng for reading/writing images with better security and performance

[syoyo]

Describe the issue

TinyGLTF currently uses stb_image, stb_image_write for reading/writing images.
STB library is easy to use and embed, but has some security issues and slow to decode/encode(especially PNG)

• wuffs https://github.com/google/wuffs
• fpng https://github.com/richgel999/fpng

are good alternative for reading/writing images with security/performance considered.

Support matrix

• JPEG decoding: wuffs
• JPEG encoding: No support in wuffs. We still need stb_image_write to encode JPEG
• PNG decoding: wuffs or fpng
• PNG encodng: fpng

Expected behaviour

Add support to use wuffs and fpng(for PNG) for better security and performance.
We also need a compile flag to disable using SIMD instrinsic for portability.

• Add compile option to on/off SIMD instrinsics for better portablity
  • fpng: https://github.com/richgel999/fpng/blob/main/src/fpng.cpp#L25
  • wuffs: WUFFS_CONFIG__AVOID_CPU_ARCH

[syoyo]

wuffs jpeg decoder has been implemented: https://github.com/google/wuffs/blob/main/doc/std/image-decoders.md

Use wuffs-unsupported-snapshot.c for a while: https://github.com/google/wuffs/blob/main/release/c/wuffs-unsupported-snapshot.c
(v0.3 does not support JPEG decoding)

[syoyo]

Created wuffs branch: https://github.com/syoyo/tinygltf/tree/wuffs