Cloning _customState: clones don't inherit correct pen state

[cwillisf]

Expected Behavior

When a rendered target is cloned, the new clone should inherit the pen state of the original. That includes:

• the size and color of the pen,
• whether the pen is down or not,
• and the events which implement drawing on move.

We should implement this in such a way that the cloning code doesn't have to "know about" pen implementation details. Ideally we should allow a block package to decide how to clone its custom state to a new target.

Actual Behavior

As of #555 we are now cloning the contents of a rendered target's _customState when that target is cloned. This means we're cloning the size and color of the pen, as well as the flag indicating whether or not the pen is down, but we're not cloning the events. This means that pen projects involving clones often behave incorrectly.

There may also be audio-related consequences, since the audio effects use _customState as well.

Steps to Reproduce

See Also

Previous issues: #481, #493
Previous discussion: #525
Current partial solution: #555