a11yclick: new press and release events

[bill]

Add synthetic events "press" and "release" to dijit/a11yclick that fire for mousedown/mouseup, touchstart/touchend (or Microsoft equivalents), or keydown/keyup. They only call the listener when the events will trigger a click. I.E. for keyboard, it's the SPACE or ENTER key, and for mouse, it's the left mouse button.

This can be useful to multiple modules:

• _HasDropDown
• tree/_dndSelector
• _CssStateMixin

[bill]

Actually this is already fixed, but I figured it should have it's own ticket.

[30807] created the new synthetic events and updated _CssStateMixin to use them.

[30808] updated tree/_dndSelector to use the new events.

[bill]

PS: I decided not to use it for _HasDropDown. The handling there is (by design) different for mouse vs. keyboard, because on mouse the mousedown opens the menu, but on keyboard it waits for the mouseup.