feat: add support to ETC1 encode/decode

[RodrigoDornelles]

It is mandatory to add a codec to compress images in ETC1 via CPU, preferably accelerated via x86 SIMD and Arm Neon (optional). An ETC1 decoder is also optional.

Find the best library that suits your maintenance needs, and upgrade the project to C++ if necessary.

some libraries:

• https://github.com/hglm/detex
• https://github.com/Ericsson/ETCPACK
• https://github.com/richgel999/rg-etc1
• https://github.com/google/etc2comp
• https://github.com/SergeyMakeev/Goofy
• https://github.com/binomialLLC/basis_universal
• https://github.com/KhronosGroup/KTX-Software
• https://github.com/GameTechDev/ISPCTextureCompressor