Adds a getter for the draggers on gesture (#4844)

core/gesture.js

@@ -968,6 +968,23 @@ Blockly.Gesture.prototype.getInsertionMarkers = function() {
   return [];
 };
 
+/**
+ * Gets the current dragger if an item is being dragged. Null if nothing is
+ * being dragged.
+ * @return {!Blockly.WorkspaceDragger|!Blockly.BubbleDragger|!Blockly.IBlockDragger|null}
+ *    The dragger that is currently in use or null if no drag is in progress.
+ */
+Blockly.Gesture.prototype.getCurrentDragger = function() {
+  if (this.isDraggingBlock_) {
+    return this.blockDragger_;
+  } else if (this.isDraggingWorkspace_) {
+    return this.workspaceDragger_;
+  } else if (this.isDraggingBubble_) {
+    return this.bubbleDragger_;
+  }
+  return null;
+};
+
 /**
  * Is a drag or other gesture currently in progress on any workspace?
  * @return {boolean} True if gesture is occurring.