fix lastClipRect and the canvas_filter shader.

Runtime/Resources/UIWidgets_canvas.cginc

      half4 color = half4(0, 0, 0, 0);
      
      float2 coord = i.ftcoord - _mf_radius * _mf_imgInc;
-     int width = _mf_radius * 2 + 1;
+     int width = _mf_radius * 2.0 + 1; // use 2.0 to avoid "bitfieldInsert"
+     
+     [unroll(25)]
      for (int i = 0; i < width; i++) {
         color += tex2D(_tex, coord) * _mf_kernel[i];
         coord += _mf_imgInc;

Runtime/ui/painting/canvas_impl.cs

         
         readonly List<RenderLayer> _layers = new List<RenderLayer>();
         RenderLayer _currentLayer;
+        Rect _lastScissor;
         
         public PictureFlusher(RenderTexture renderTexture, float devicePixelRatio, MeshPool meshPool) {
             D.assert(renderTexture);
         }
         
         void _tryAddScissor(RenderLayer layer, Rect scissor) {
-            if (scissor == layer.lastScissor) {
+            if (scissor == this._lastScissor) {
                 return;
             }
 
-            layer.lastScissor = scissor;
+            this._lastScissor = scissor;
         }
         
         bool _applyClip(Rect queryBounds) {
             public readonly ClipStack clipStack = new ClipStack();
             public uint lastClipGenId;
             public Rect lastClipBounds;
-            public Rect lastScissor;
             public bool ignoreClip = true;
 
             Vector4? _viewport;