feat: add vaapi path for video wallpapers on generic gpus

Plugins/ZShell/Wallpaper/shaders/wallpaper_trans_wipe_down.frag

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+// Hard-edged wipe from top to bottom, from gl-transitions.com
+// Author: Jake Nelson (MIT)
+//
+// Ported to ZShell's GLSL ABI (see wallpaper_trans_bowtie.frag).
+
+uniform sampler2D from;
+uniform sampler2D to;
+uniform vec2 size;
+uniform vec4 fromCrop;
+uniform vec4 toCrop;
+uniform float progress;
+uniform float fromFlip;
+uniform float toFlip;
+
+out vec4 outColor;
+
+vec4 getFromColor(vec2 uv) {
+	vec2 s = vec2(uv.x, fromFlip > 0.5 ? 1.0 - uv.y : uv.y);
+	return texture(from, fromCrop.xy + s * fromCrop.zw);
+}
+
+vec4 getToColor(vec2 uv) {
+	vec2 s = vec2(uv.x, toFlip > 0.5 ? 1.0 - uv.y : uv.y);
+	return texture(to, toCrop.xy + s * toCrop.zw);
+}
+
+vec4 transition(vec2 uv) {
+	return mix(getFromColor(uv), getToColor(uv), step(1.0 - uv.y, progress));
+}
+
+void main() {
+	vec2 uv = gl_FragCoord.xy / size;
+	outColor = transition(uv);
+}