WEBP image format support

[MajorMurphy]

I've included libwebp 07b7185, which closes #274

Supports decoding and encoding 24-bit and 32-bit RGB and ARGB images.

Encoding by default is lossless. However lossy encoding is possible by calling WEBPImageFormat::setQuality(bool shouldBeLossless, float newQuality). The quality value range is 0 - 1.0, same as JPEGImageFormat::setQuality.

Tested building with

• MSVC 2022
• Android 13 SDK
• gcc 12.3.0 (Ubuntu 23.04)
• XCode 12.4