Make MonitorAwarePoint a windows-specific implementation detail

[nedtwigg]

• Use monitor-aware coordinates in multi-zoom coordinate system #1711 made Point and Rectangle part of a sealed class hierarchy which added MonitorAware variants
• this new hierarchy causes two problems
  • users cannot instantiate Point or Rectangle from Kotlin, because Kotlin does not allow the base of a sealed hierarchy to be one of the elements
  • even for Java users, equality is now muddled. Two points can have the same x, y values, but not be equal. For example, take a point, map it to a control, map it back, you'll get the same coordinates you started with, but .equals will be false now because one of the points will be a MonitorAware. This behavior only happens on Windows.

I'm proposing two PRs. This, the first one, doesn't fix the muddled equality bug, but it makes MonitorAware a package-private implementation detail that only affects the win32 platform.

The second one (#1904) removes MonitorAware and replaces it with logic that is contained within the MultiZoomCoordinateMapper. As of SWT in the release 4.35, these new MonitorAware variants are created in exactly two places.

• eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/MultiZoomCoordinateSystemMapper.java

  Line 155 in e1f11c9

  MonitorAwareRectangle rect = new MonitorAwareRectangle(topLeft.x, topLeft.y, width, height, monitor);

• eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/MultiZoomCoordinateSystemMapper.java

  Line 264 in e1f11c9

  return new MonitorAwarePoint(mappedX, mappedY, monitor);

[HeikoKlare]

Unfortunately, this is not possible for multiple reasons:

1. The MonitorAware... classes are used from another package, so this change does not compile. We also wanted to make both the coordinate system mappers as well as the monitor-aware classes internal, but there is unfortunately no JLS-conforming way to do that, so we decided to make the monitor-aware classes public but marking them as @noreference.
2. Point and Rectangle were final and are not supposed to be subclassed in an unexpected way (i.e., outside SWT). That's why sealed types are a valid replacement but just removing the final modifier is not.

[nedtwigg]

• closing in favor of Take MonitorAware out of the geometry hierarchy with as few other changes as possible #1905