Make accessibleNameBehavior work without a tagName

[jessegreenberg]

From phetsims/scenery-phet#880, I found that accessibleNameBehavior only works if you specify a tagName.

For many use cases, accessibleNameBehavior will be useful for forwarding the accessibleName to a subcomponent, where the parent component should not have any PDOM content.

If accessibleNameBehavior can work without a tagName it will save the PDOM from having lots of extra divs and developers from spending time trying to figure out why accessibleNameBehavior isn't working.

[jessegreenberg]

This won't be simple. Accessibility in scenery has always assumed that tagName is the 'entry point' for all ParallelDOM options.

[jessegreenberg]

This change is too large, so I am going to close. Instead, I made some helper functions for forwarding the accessible Name and using those will set a default tagName, see #1665. Closing.