Add support for dynamic locale

[pixelzoom]

... similar to what was done in phetsims/natural-selection#319.

This also includes ph-scale-basics.

[pixelzoom]

Code specific to ph-scale-basics was completed in the above commit.

[pixelzoom]

Next on my list, so raising priority.

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Before doing this work, I published 1.6.0-dev.3 for brands=phet,phet-io as a baseline.

[pixelzoom]

In the above commits, I did the low-hanging fruit -- the StringProperties that are passed directly to a Text/RichText constructor.

I can already tell that this sim is going to have significant layout problems.

[pixelzoom]

@arouinfar ready for review.

[arouinfar]

@pixelzoom overall things look good in ph-scale. I didn't review the links to the StringProperties in the view components, since it sounds like that work is still outstanding. Let me know if you need any guidance before you begin.

I found a few issues with dynamic layout:

1. pHStringProperty - the text does not remain centered and escapes the bounds of the pH Meter.
   
2. phScale.microScreen.view.beakerControlPanel.separator does not change in size when the panel expands to accommodate long strings. Not sure if this is something that can be handled within the scope of dynamic layout, but wanted to point it out in case this behavior is unexpected or can be corrected. (Feel free to veto if overly complicated.)
   

In ph-scale-basics, I'm seeing every single ph-scale string. Since there isn't a way to re-add the additional screens in Basics, these strings seem completely irrelevant. For example, many of these StringProperties relate to later screens.

I wasn't sure how this was being handled in rosetta, so I compared to the Translation Utility. The strings specific to pH Scale (e.g. linearStringProperty or moleculeCountStringProperty) do not appear.

[pixelzoom]

1. and 2. above are certainly things that can be addressed. Thanks for identifying.

In ph-scale-basics, I'm seeing every single ph-scale string. ...

This is a general problem, not specific to ph-scale-basicis. A sim's PhET-iO API currently includes every string Property, from every dependency repo, regardless of whether those strings are using in the sim. Tracking in https://github.com/phetsims/phet-io/issues/1877.

[pixelzoom]

I've created separate issues for each things that @arouinfar reported in #239 (comment). Closing.