Usability on small screens review

[KatieWoe]

Per @kathy-phet's request in phetsims/qa#295 I am making issues in each published sim repo detailing the pointer areas and usability of sims on phone sized screens. Done on an iPhone 7 iOS 12 device.

Potential Difficulties Noticed:

• When pause/play button is play, the pointer areas overlap a bit. (I believe this has already been solved)
• I found it quite difficult to switch between Kelvin and Celsius
  The +/- zoom buttons on the last screen could sometimes be a bit difficult

Screenshots:

[KatieWoe]

Also, should the pump have touchSnag?

[arouinfar]

Thanks @KatieWoe.

When pause/play button is play, the pointer areas overlap a bit. (I believe this has already been solved)

This does not appear to be an issue in master.

I found it quite difficult to switch between Kelvin and Celsius

We may be somewhat constrained by the bounds of the ComboBox. @jbphet can you look into this?
I tested on my phone, and didn't have any difficulty, so I would be fine with leaving as-is, if necessary.

The +/- zoom buttons on the last screen could sometimes be a bit difficult

RectangularButtonView does not support asymmetric pointer area dilation, but it is being considered in phetsims/sun#500. An alternative option would be to move the zoom out button down a bit to allow for larger pointer area dilation. I'll defer to @jbphet.

Here's a mockup of an asymmetric dilation.

Also, should the pump have touchSnag?
Should touchSnag be on the atoms? [suggested in https://github.com/phetsims/atomic-interactions/issues/78]

If touchSnag is something that can be quickly added, then I'd be in favor. Otherwise, the touch areas seem generous enough as-is, so I'll leave it up to @jbphet.

[SaurabhTotey]

I haven't changed the kelvin-celsius conversion ComboBox. I have, however, given the zoom buttons on the last screen an asymmetric dilation that looks like the below image in master.

Also, the particles in the last screen (the large draggable one at the bottom and the marker on the graph) now have touch snag. I believe the bike pump has touch snag by default; when I tested it, it seemed to have touch snag.

[arouinfar]

Looks good @SaurabhTotey, thanks!

[KatieWoe]

Relevent changes seem to be made in phetsims/qa#525, though buttons in #243 (comment) have been removed. Closing for now. Will reopen if problems show up.