Add spinner glow resources

osu.Game.Resources/Shaders/sh_SpinnerGlow.fs

@@ -0,0 +1,49 @@
+#ifndef SPINNER_GLOW_FS
+#define SPINNER_GLOW_FS
+
+#undef HIGH_PRECISION_VERTEX
+#define HIGH_PRECISION_VERTEX
+
+#include "sh_Utils.h"
+#include "sh_Masking.h"
+#include "sh_CircularProgressUtils.h"
+
+layout(location = 2) in highp vec2 v_TexCoord;
+
+layout(std140, set = 0, binding = 0) uniform m_ProgressGlowParameters
+{
+    mediump float innerRadius;
+    mediump float progress;
+    highp float texelSize;
+    highp float glowSize;
+};
+
+layout(set = 1, binding = 0) uniform lowp texture2D m_Texture;
+layout(set = 1, binding = 1) uniform lowp sampler m_Sampler;
+
+layout(location = 0) out vec4 o_Colour;
+
+void main(void)
+{
+    highp vec2 resolution = v_TexRect.zw - v_TexRect.xy;
+
+    // Inflate coordinate space, so it would be (-glowSize -> 0 -> 1 -> glowSize) to preserve everything in place while inflating the draw quad
+    highp vec2 pixelPos = (v_TexCoord - v_TexRect.xy) / resolution * (vec2(1.0) + glowSize * 2.0) - glowSize;
+
+    highp float dst = distanceToProgress(pixelPos, progress, innerRadius, true, texelSize);
+    highp float progressThickness = innerRadius * 0.25;
+    highp float relativeTextureHeight = glowSize + progressThickness;
+
+    if (dst > relativeTextureHeight)
+    {
+        o_Colour = vec4(0.0);
+        return;
+    }
+
+    highp float textureY = 1.0 - (dst / relativeTextureHeight);
+    lowp vec4 texCol = texture(sampler2D(m_Texture, m_Sampler), v_TexRect.xy + vec2(0.0, textureY) * resolution, -0.9);
+
+    o_Colour = getRoundedColor(texCol, v_TexCoord);
+}
+
+#endif