Dock, Tray, ActiveWindow, Taskbar: add theming for app/tray icons

appicon_colorize: create simple shader to colorize icons by theme color

Shaders/frag/appicon_colorize.frag

@@ -0,0 +1,29 @@
+#version 450
+layout(location = 0) in vec2 qt_TexCoord0;
+layout(location = 0) out vec4 fragColor;
+layout(binding = 1) uniform sampler2D source;
+layout(std140, binding = 0) uniform buf {
+    mat4 qt_Matrix;
+    float qt_Opacity;
+    vec4 targetColor;
+    float colorizeMode; // 0.0 = dock mode (grayscale), 1.0 = tray mode (intensity)
+} ubuf;
+
+void main() {
+    vec4 tex = texture(source, qt_TexCoord0);
+    
+    float intensity;
+    
+    if (ubuf.colorizeMode < 0.5) {
+        // Dock mode: Convert to grayscale using proper luminance weights
+        intensity = dot(tex.rgb, vec3(0.299, 0.587, 0.114));
+    } else {
+        // Tray mode: Use the maximum RGB channel value as intensity
+        intensity = max(max(tex.r, tex.g), tex.b);
+        
+        // Normalize intensity to make all icons more uniform
+        intensity = smoothstep(0.1, 0.9, intensity);
+    }
+    
+    fragColor = vec4(ubuf.targetColor.rgb * intensity, tex.a) * ubuf.qt_Opacity;
+}