Proposed v0.29.0 "circle" release: faster AVIF encoding, drop Node.js 10 support

[lovell]

Updates to the prebuilt binaries include:

• Upgrade to forthcoming libvips v8.11.3 for improved multi-threaded performance on Windows (up to ~15%)
• Patch libheif for ~2x faster AVIF encoding
• Reduced binary size, ~12% smaller

Potentially breaking changes:

• AVIF encoding will default to 4:4:4 (i.e. without) chroma subsampling - Enhancement: control AVIF subsampling to reduce blockiness on high contrast edges #2562
• Upgrade to Node-API (N-API) version 5
• Drop support for Node.js 10, minimum Node.js version will be 12.13.0 (LTS)
• extractChannel will default to single-channel (rather than sRGB) - Extracting alpha channel yields triple the bytes #2658

Other possible improvements:

• Install prebuilt libvips binaries into platform-arch subdirectories under vendor/x.y.z/ - Allow install of many platform binaries in same worktree #2575
• Expose heif compression e.g. AV1, HEVC in metadata output - Metadata for AVIF, format returned as 'heif' #2504
• Optional wider-gamut processing - Add pipelineColourspace operator #2704
• Always use Brotli-compressed tarballs for prebuilt libvips binaries

[lovell]

https://packagephobia.com/result?p=sharp suggests the install size for the latest version is less than 20MB 🎉