Create/Update assets for version 1.21-pre3

assets/minecraft/shaders/core/position.vsh

@@ -0,0 +1,17 @@
+#version 150
+
+#moj_import <fog.glsl>
+
+in vec3 Position;
+
+uniform mat4 ProjMat;
+uniform mat4 ModelViewMat;
+uniform int FogShape;
+
+out float vertexDistance;
+
+void main() {
+    gl_Position = ProjMat * ModelViewMat * vec4(Position, 1.0);
+
+    vertexDistance = fog_distance(Position, FogShape);
+}