Add Kuwahara Filter, implements #49

examples/images/mountain.jpg.import

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+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://ben72llmopgaj"
+path="res://.godot/imported/mountain.jpg-c1b7de1e6557b826bc6f9324027e11af.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://examples/images/mountain.jpg"
+dest_files=["res://.godot/imported/mountain.jpg-c1b7de1e6557b826bc6f9324027e11af.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1

examples/kuwahara.gdshader

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+shader_type canvas_item;
+
+//!load ./images/mountain.jpg
+
+#include "res://shaderlib/kuwahara.gdshaderinc"
+#include "res://shaderlib/hsv.gdshaderinc"
+
+void fragment() {
+	// Kuwahara
+	COLOR.rgb = kuwahara(TEXTURE, UV, 20, 80.0, 18.0, 0.6, .15, 8);
+	// A litte bit of color adjustments
+	vec4 hsv = rgb2hsv(COLOR);
+	hsv.x += .03;
+	hsv.y *= 1.4;
+	COLOR = hsv2rgb(hsv);
+}