[no sq] Move shaders & remove dead Irrlicht tests (#15006)

* Move irrlicht shaders to correct place

* Remove unused Irrlicht tests

client/shaders/Irrlicht/TransparentAlphaChannel.fsh

@@ -0,0 +1,69 @@
+#version 100
+
+precision mediump float;
+
+/* Uniforms */
+
+uniform float uAlphaRef;
+uniform int uTextureUsage0;
+uniform sampler2D uTextureUnit0;
+uniform int uFogEnable;
+uniform int uFogType;
+uniform vec4 uFogColor;
+uniform float uFogStart;
+uniform float uFogEnd;
+uniform float uFogDensity;
+
+/* Varyings */
+
+varying vec2 vTextureCoord0;
+varying vec4 vVertexColor;
+varying float vFogCoord;
+
+float computeFog()
+{
+	const float LOG2 = 1.442695;
+	float FogFactor = 0.0;
+
+	if (uFogType == 0) // Exp
+	{
+		FogFactor = exp2(-uFogDensity * vFogCoord * LOG2);
+	}
+	else if (uFogType == 1) // Linear
+	{
+		float Scale = 1.0 / (uFogEnd - uFogStart);
+		FogFactor = (uFogEnd - vFogCoord) * Scale;
+	}
+	else if (uFogType == 2) // Exp2
+	{
+		FogFactor = exp2(-uFogDensity * uFogDensity * vFogCoord * vFogCoord * LOG2);
+	}
+
+	FogFactor = clamp(FogFactor, 0.0, 1.0);
+
+	return FogFactor;
+}
+
+void main()
+{
+	vec4 Color = vVertexColor;
+
+	if (bool(uTextureUsage0))
+	{
+		Color *= texture2D(uTextureUnit0, vTextureCoord0);
+
+		// TODO: uAlphaRef should rather control sharpness of alpha, don't know how to do that right now and this works in most cases.
+		if (Color.a < uAlphaRef)
+			discard;
+	}
+
+	if (bool(uFogEnable))
+	{
+		float FogFactor = computeFog();
+		vec4 FogColor = uFogColor;
+		FogColor.a = 1.0;
+		Color = mix(FogColor, Color, FogFactor);
+	}
+
+	gl_FragColor = Color;
+}