Create/Update assets for version 1.17-pre4

assets/minecraft/shaders/include/light.glsl

@@ -0,0 +1,17 @@
+#version 150
+
+#define MINECRAFT_LIGHT_POWER   (0.6)
+#define MINECRAFT_AMBIENT_LIGHT (0.4)
+
+vec4 minecraft_mix_light(vec3 lightDir0, vec3 lightDir1, vec3 normal, vec4 color) {
+    lightDir0 = normalize(lightDir0);
+    lightDir1 = normalize(lightDir1);
+    float light0 = max(0.0, dot(lightDir0, normal));
+    float light1 = max(0.0, dot(lightDir1, normal));
+    float lightAccum = min(1.0, (light0 + light1) * MINECRAFT_LIGHT_POWER + MINECRAFT_AMBIENT_LIGHT);
+    return vec4(color.rgb * lightAccum, color.a);
+}
+
+vec4 minecraft_sample_lightmap(sampler2D lightMap, ivec2 uv) {
+    return texture(lightMap, clamp(uv / 256.0, vec2(0.5 / 16.0), vec2(15.5 / 16.0)));
+}