Changes

UpstreamSurfaceHook: Add 'NativeSurface getUpstreamSurface()' (from EGLUpstreamSurfaceHook) to generalize ProxySurfaceImpl.getUpstreamSurface()

Minor: API-Doc / DEBUG Typo, GDISurface: Make fields private

Bug 741 HiDPI: Add ScalableSurface interface to get/set pixelScale w/ full OSX impl.

Add ScalableSurface interface
  - To set pixelScale before and after realization
  - To get pixelScale

  - Implemented on:
    - NEWT Window
      - Generic impl. in WindowImpl
      - OSX WindowDriver impl.
        - Also propagetes pixelScale to parent JAWTWindow if offscreen (NewtCanvasAWT)
      - AWT WindowDriver impl.

    - JAWTWindow / OSXCalayer
      - AWT GLCanvas
      - AWT GLJPanel
      - NEWTCanvasAWT:
        - Propagates NEWT Window's pixelScale to underlying JAWTWindow

    - WrappedSurface for pixelScale propagation
      using offscreen drawables, i.e. GLJPanel

    - Generic helper in SurfaceScaleUtils (nativewindow package)

  - Fully implemented on OSX

  - Capable to switch pixelScale before realization,
    i.e. native-creation, as well as on-the-fly.

  - Impl. uses int[2] for pixelScale to support
    non-uniform scale.

Test cases:
  - com.jogamp.opengl.test.junit.jogl.demos.es2.newt.TestGearsES2NEWT
  - com.jogamp.opengl.test.junit.jogl.demos.es2.awt.TestGearsES2AWT
  - com.jogamp.opengl.test.junit.jogl.demos.es2.awt.TestGearsES2GLJPanelAWT
  - com.jogamp.opengl.test.junit.jogl.demos.es2.newt.TestGearsES2NewtCanvasAWT

  - Press 'x' to toggle HiDPI
  - Commandline '-pixelScale <value>'
  - Added basic auto unit test (setting pre-realization)

Bug 741 HiDPI: Simplify ScalableSurface [set|get]SurfaceScale(..) spec, which also fixed JAWTWindow getSurfaceScale() issue on Windows

Let setSurfaceScale(..) return the validated requested values
and getSurfaceScale(..) always the current values.

This removes complication and solves a bug w/ JAWTWindow on Windows,
where we used 'drawable' as an indicator for 'previous locked' state.
The latter is not true since on Windows 'drawable' is set to null in unlock,
getWindowHandle() should be taken instead.