MouseEvent: Clarify 'Multiple-Pointer' w/ button[mask] semantics, ; InputEvent: getButtonDownCount() and isAnyButtonDown();

- Clarify 'Multiple-Pointer' w/ button[mask] semantics

  - Pointer IDs start w/ 0 and are consecutive numbers.

  - 'button' == triggering pointer-ID

  - buttonMask in modifiers show pressed button _and_ pointer-IDs

- deprecated BUTTON_NUMBER -> use BUTTON_COUNT (name semantics)
Int -> Enum using EnumClass.values()[ordinal] instead of for-loop - FFMPEGNatives's Enums and new MouseEvent.PointerType.valueOf(int)
NEWT PointerEvent: Unify event processing in new doPointerEvent(..) and consumePointerEvent(..) - Unifies native mouse and Android's pointer event, ready for Win7 touch

Unify event processing in new doPointerEvent(..), which is also invoked from doMouseEvent(..),
and consumePointerEvent().

doPointerEvent(..): Validates and modifies event data and finally creates the event,
where consumePointerEvent(..) calls gesture handlers and may synthesize events.

Unifies native mouse and Android's pointer event, ready for Win7 touch.
AndroidNewtEventFactory calls doPointerEvent(..) directly.

Removed lots of duplicated pointer event handling code.
PinchToZoomGesture: Validate pointer-IDs, skip if invalid.