getModifiers() always returns null for ActionEvents.

It should either be made to work, or deprecated.

Here is a comment from Amy on this:

In truth I don't think modifiers belong in ActionEvents (they
are supposed to be higher level than a raw input event).

The reason that property is there is to support backward compatibility
with the old event model where modifiers were supported for action
events (it was some wierd hotjavaism).

But as you can see, they don't even work anyways. So, I suggest
we deprecate getModifiers() on ActionEvent....