Pickable should work with a11y listeners

[jessegreenberg]

After #888, it may be possible to use pickable with a11y listeners. We currently have checks in individual listeners against enabledProperty to determine whether or not to run functionality in the listener. It would be great if we could enable/disable this directly through pickable or some other a11y equivalent.

Referencing @zepumph in case he has any thoughts but we probably won't get to this for a little while.

[jessegreenberg]

After #888 I was wondering if this was working for us for free, but I tested and observed that we are hitting listeners from a11y input when a Node has pickable false.

[zepumph]

I believe that we have this implemented. Both inputEnabled and pickable are respected by the PDOM-specific events in Input.js.

Here is where we are making sure that pickable is respeced for PDOM input:

scenery/js/input/Input.js

Lines 1055 to 1058 in a7bfc37

	// If the trail is not pickable, don't dispatch PDOM events to those targets - but we still
	// dispatch with an empty trail to call listeners on the Display and Pointer.
	const canFireListeners = trail.isPickable() || PDOM_UNPICKABLE_EVENTS.includes( eventType );

Note that events like focus/blur still fire. @jessegreenberg is there anything else to discuss for this issue? Or can we close it?

[zepumph]

This issue is very old at this point. A11y listeners have been working well for a long time, and focus/blur are needed to provide keyboard navigation on disabled elements. I believe that we may need to improve this logic more generally over in #1220, but for now. I think we are ready to close.