problems with FeedbackWindow and subclasses

[pixelzoom]

Noted while converting to ES6 class in https://github.com/phetsims/tasks/issues/1049.

• [x] Subclasses YouBuiltWindow and YouEnteredWindow pass options by both super(...,options) and this.mutate( options ). This is an anti-pattern that can get you into trouble with transform-related options. Pass options once, using one of these methods.

• [x] FeedbackWindow goes to the trouble of calling options = merge( {...}, options ), then does not pass options to super.

Low priority, but worth fixing at some point.

[jbphet]

For the first item above, I removed the calls to .mutate and the behavior was unchanged. For the second, I changed the call to the superconstructor to pass in the options instead of the decomposed options that it was using, and that appears to have worked too.

I tested using number, short, and long strings, and the position of the YouBuiltWindow and the YouEnteredWindow was unchanged.

Seems like that should do it. Closing.