Create/Update assets for version 1.21.5-pre2

assets/minecraft/shaders/core/gui.vsh

@@ -0,0 +1,15 @@
+#version 150
+
+in vec3 Position;
+in vec4 Color;
+
+uniform mat4 ModelViewMat;
+uniform mat4 ProjMat;
+
+out vec4 vertexColor;
+
+void main() {
+    gl_Position = ProjMat * ModelViewMat * vec4(Position, 1.0);
+
+    vertexColor = Color;
+}