VM changes for the sensing_of block. This handles lists properly (by ignoring them like Scratch2 and makes the attribute menu update based on what was chosen in the target menu.

src/engine/runtime.js

@@ -613,6 +613,14 @@ class Runtime extends EventEmitter {
         return 'RUNTIME_STARTED';
     }
 
+    /**
+     * Event name for reporting that a block was updated and needs to be rerendered.
+     * @const {string}
+     */
+    static get BLOCKS_NEED_UPDATE () {
+        return 'BLOCKS_NEED_UPDATE';
+    }
+
     /**
      * How rapidly we try to step threads by default, in ms.
      */
@@ -2169,6 +2177,13 @@ class Runtime extends EventEmitter {
         this._refreshTargets = true;
     }
 
+    /**
+     * Emit an event that indicate that the blocks on the workspace need updating.
+     */
+    requestBlocksUpdate () {
+        this.emit(Runtime.BLOCK_NEED_UPDATE);
+    }
+
     /**
      * Set up timers to repeatedly step in a browser.
      */