Use findStringProperty to automatically discover accessible names

[jessegreenberg]

In phetsims/scenery#1526, a utility function was added that can find string Properties under a Node. Called PDOMUtils.findStringProperty. It can be used to set default accessible names for common code components.

This issue is to review components in sun, scenery-phet, and other common code components and use this utility function to implement good defaults for accessible names.

Related to #901.

[jessegreenberg]

We are going to try using this to support MOTHA. Here is a list of components that we should start with for this work.

phetsims/models-of-the-hydrogen-atom#82 (comment)

[jessegreenberg]

Doing this in ComboBox will be a bit tricker because of changes for #865. I have asked if we can remove some of that code. In the meantime I'll work on other components.

EDIT: Confirmed that it is OK to remove this code. That will clean up ComboBox and make it easier to implement this issue.

[jessegreenberg]

The above commits handle components that were needed for MOTHA.