wallpapers/color: better accent color generator from Android

The accent color is extracted using the Android method, which includes:

1. Wu's quantization algorithm
2. K-Means for color quantization by Celebi
3. A color appearance model based on CAM16
4. Color scores based on hue proportions and chroma.

Then a dominant color is extracted from the clusters, and the final color will be adjusted to be not too dark or too light.

Reference: https://doi.org/10.1016/j.imavis.2010.10.002

The Celebi color quantizer is transformed from

• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/palette/CelebiQuantizer.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/palette/WSMeansQuantizer.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/palette/WuQuantizer.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/palette/QuantizerMap.java

The color appearance model and the color score formula are transformed from:

• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/android/app/WallpaperColors.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/ColorUtils.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/cam/CamUtils.java
• https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/java/com/android/internal/graphics/cam/Frame.java

BUG: 457861 FIXED-IN: 5.26

Requires: plasma-desktop!1106 (merged)

@tantalising