Webgl points / get back the instructions array from the worker

This means we won't have to recreate a binary buffer (through a typed array)
on every `rebuildBuffer` call.

src/ol/renderer/webgl/PointsLayer.js

@@ -291,6 +291,8 @@ class WebGLPointsLayerRenderer extends WebGLLayerRenderer {
         // saves the projection transform for the current frame state
         this.renderTransform_ = projectionTransform;
         makeInverseTransform(this.invertRenderTransform_, this.renderTransform_);
+
+        this.renderInstructions_ = new Float32Array(event.data.renderInstructions);
       }
     }.bind(this));
   }

src/ol/worker/webgl.js

@@ -30,8 +30,9 @@ onmessage = event => {
       type: 'buffers-generated',
       vertexBuffer: vertexBuffer.buffer,
       indexBuffer: indexBuffer.buffer,
+      renderInstructions: renderInstructions.buffer,
       projectionTransform
-    }, [vertexBuffer.buffer, indexBuffer.buffer]);
+    }, [vertexBuffer.buffer, indexBuffer.buffer, renderInstructions.buffer]);
   }
 };