Introduce DisplayObject#_containsGlobalPoint and don't use Point in that or _containsPoint

Reduces the amount of garbage created during hit testing quite drastically.
Correctly apply transform of hitTestState when hit-testing SimpleButton
Make the `flash` build target depend on `swf.d.ts` to be able to use Stream

Stream can probably be removed completely, but for now this'll do.
Rename DisplayObject#_containsGlobalPoint to _isUnderMouse and stop using it in hitTestPoint

That way, it can be overridden in SimpleButton without `hitTestPoint` giving wrong results for that: that method mustn't take the hitTestState into account.