Create/Update assets for version 21w18a

assets/minecraft/shaders/core/blit_screen.fsh

@@ -0,0 +1,17 @@
+#version 150
+
+uniform sampler2D DiffuseSampler;
+
+uniform vec4 ColorModulator;
+
+in vec2 texCoord;
+in vec4 vertexColor;
+
+out vec4 fragColor;
+
+void main() {
+    vec4 color = texture(DiffuseSampler, texCoord) * vertexColor;
+
+    // blit final output of compositor into displayed back buffer
+    fragColor = color * ColorModulator;
+}