Upgrade to libvips 8.10.6-alpha1

- Prebuilt binaries now include mozjpeg and libimagequant (BSD 2-Clause)
- Prebuilt binaries limit AVIF support to the most common 8-bit depth
- Add `mozjpeg` option to `jpeg` method, sets mozjpeg defaults
- Reduce the default PNG `compressionLevel` to the more commonly used 6

lib/constructor.js

@@ -244,7 +244,7 @@ const Sharp = function (input, options) {
     jpegOptimiseCoding: true,
     jpegQuantisationTable: 0,
     pngProgressive: false,
-    pngCompressionLevel: 9,
+    pngCompressionLevel: 6,
     pngAdaptiveFiltering: false,
     pngPalette: false,
     pngQuality: 100,