Performance audit for Node.phetioVisibleProperty definition in constructor

[zepumph]

From #1046 and #490 (comment):

@jonathanolson said:

[@zepmuph said] In Node.js we define this.phetioVisibleProperty. We weren't sure whether to null it out in the constructor (adding more keys to every single Node) or to lazily add it to only the Nodes that are PhET-iO instrumented. Keep in mind this will be done for opacity and pickability as well. We weren't sure whether to minimize the number of Node keys or hidden classes. It seems clearer to put them in the constructor, but we weren't sure how essential it is to minimize the number of Node attributes.

That is a really good question. Because we are inheriting from Node all the time, it complicates the hidden class question (so intuitively I think the minimization of Node keys might be better for performance/memory, but I haven't investigated that). Sounds like something good to test, to see what effect it would have.

I think this should be in a separate issue. @jonathanolson please let me know if I can help with this. Currently it is not in the Node constructor, even set to null.

[zepumph]

Over in #1087 we decided to initialize it to null in the constructor. It is now called ownedPhetioVisibleProperty. Closing