Add support for PhET-iO

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Things to consider when this sim is instrumented for PhET-iO.

EqualityExplorerMovable defines isDisposed and dispose. If it needs to extend PhetioObject, these definitions will shadow definitions in PhetioObject.

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@kathy-phet asked for an estimate to add PhET-iO instrumentation. Here it is:

It’s difficult to provide an estimate without knowing the PhET-iO requirements. But assuming that we instrument all 3 sims in this family, and assuming there’s nothing ununsual like the special query parameters in Natural Selection.. My estimate is 200-300 hours.

Here’s how I arrived at that estimate:

• pH Scale took 100+ hours to retrofit, 50% of its original cost, and it’s a relatively simple sim with no dynamic elements. So Equality Explorer is going to be > 100 hours.
• Equality Explorer has lots of dynamic elements, so complexity of the PhET-iO instrumentation is more similar to Natural Selection.
• Natural Selection 1.0 had ~25% of its cost (153 of 589 hours) dedicated to PhET-iO.
• Since Equality Explorer is a retrofit, I would expect a higher percentage than Natural Selection, somewhere between 30-50% of its original cost.
• The original cost of Equality Explorer was 634 hours. So 30-50% is ~200-300 hours.

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My understanding is that @kathy-phet would like to discuss this sometime towards the beginning of Q2 2022. So assigning to @kathy-phet and @amanda-phet.

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As we did with Natural Selection, the first phase of adding PhET-iO support needs to be design. Identify sim-specific features, provide as much information as possible to make sure that PhET-iO instrumentation is done in a way that it can support those features.

EDIT: PhET-iO design is being tracked in https://github.com/phetsims/equality-explorer/issues/191

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According to @kathy-phet in Slack, "we are going to postpone that work on EE for now". So unassigning myself, and labeling as deferred.

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@kathy-phet would like me to do the "basic" PhET-iO instrumentation for this sim; no custom IOTypes or dynamic elements, just the stuff that is straightforward. I did a little bit of that as part of TypeScript conversion #186, since some of PhET’s APIs now require tandems when used with TypeScript. This will also get me more familiar with the things that are going to be more difficult, and I'll try to note those things in this issue as I go.

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Basic PhET-iO instrumentation is being done as part of https://github.com/phetsims/equality-explorer/issues/192.

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Doing this work in https://github.com/phetsims/equality-explorer/issues/192, per the "process". Closing.