hard fix computer buffer issue (disable it by default and skip shader preparation when enablecomputebuffer = false)

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_shader.cs

             return shader;
         }
 
-        public static bool enableComputeBuffer = true;
-
-        public static bool supportComputeBuffer;
-
         static CanvasShader() {
             
         }

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_shader_initializer.cs

         static int initialFrameCount;
         static Shader testShader;
         const string testShaderName = "UIWidgets/canvas_convexFill_cb";
+        
+        
+        const bool enableComputeBuffer = false;
+
+        public static bool supportComputeBuffer;
 
         static bool OnNotPrepared() {
             initStage = InitStage.Prepared;
             var material = new Material(testShader);
             //for Unity 2018 or below, shader is compiled after Shader.Find() call immediately,
             //therefore we can just skip the manually preload if the compilation fails
-            if (!material.shader.isSupported) {
+            if (!material.shader.isSupported || !enableComputeBuffer) {
                 ObjectUtils.SafeDestroy(material);
                 return OnPrepared(true);
             }