Allow adding EventHandlers

[pauldendulk]

The problem
In 5.0.0-beta.1 it is not possible for users to add event handlers for the PointerPressed, PointerMoved, PointerReleased, Tapped events, like there is for Info. They do not exist for the MapControl and for Widgets.

The proposed solution
They need to be added. For widgets I was thinking to add them to the BaseWidget so that all widgets handle all events. Questions:

• Should they be weak references. Would this mean an assigned lambda could be cleaned up?
• How should they be named? For the MapControls the names above will collide with existing events. And for widgets we could use the names above, but perhaps we want the same names for the MapControl and the Widgets. Some options:
  • MapPointerPressed
  • MapsuiPointerPressed
  • MPointerPressed
  • MapPointerPressed and WidgetPointerPressed
  • MapPointerPressed and PointerPressed
• With all events on a TextBoxWidget it would become identical to a ButtonWidget. Is this is a problem?