Demo showing the "stack click threads and hat threads can coexist" behavior of Runtime.startHats. This shows precedent for more than one thread of the same script/hat executing (existing) simultaneously. (Please note you can't start more than two threads with this mechanism. Clicking the "broadcast" block twice will just reset the existing non-click thread - note how the sprite never moves faster than 2 * 2 units per frame.) https://github.com/LLK/scratch-vm/blob/93780400cd05ce9da2c081ac0f3c96fbb6a5af01/src/engine/runtime.js#L1810-L1835
