Implement QuantizeColorsModifier::class

[olivervogel]

Describe the feature you'd like

Implementation of Intervention\Image\Drivers\Vips\Modifiers\QuantizeColorsModifier::class. Used in Image::reduceColor()

It is currently unclear whether this is even possible with libvips. Color reduction/quantization could only be possible in the encoding output via the bit-depth AFAIK.

[olivervogel]

I could not find any information. Asked at php-vips.

[olivervogel]

Currently not possible. But there is a PR and will probably be integrated soon.