move noise shader into shaders folder

assets/shaders/noise.gdshader

@@ -0,0 +1,19 @@
+shader_type canvas_item;
+
+uniform bool animate_noise = false;
+uniform float noise_intensity = 1.0;
+uniform float fps = 60.0;
+
+float random (vec2 uv) {
+    return fract(sin(dot(uv.xy,
+        vec2(12.9898,78.233))) * 43758.5453123);
+}
+
+void fragment() {
+	float time = floor(fract(TIME) * fps);
+	vec2 noise_uv = SCREEN_UV + time * float(animate_noise);
+	float noise = random(noise_uv);
+	noise = mix(1.0 - noise_intensity, 1.0, noise);
+
+	COLOR = vec4(COLOR.rgb * noise, COLOR.a);
+}