Fix display of context menu in ContextMenusOnShapes demo. (#274)

* Fix display of context menu in ContextMenusOnShapes demo.  Retain copy of AWT screen coordinate when creating SelectEvent.

* Fixes for drag and drop when DPI scaling in use, reported by https://github.com/NASAWorldWind/WorldWindJava/pull/274#issuecomment-1883373775

* Correct clamping of mouse position to viewport coordinates;  previous edition has used AWT size of canvas, and mouse positions from MouseEvents are converted to GL surface coordinates early on.

* Make pitch change of globe using right mouse work as it did before DPI scaling changes.  Moving the mouse down should increase the pitch, so it appears that the top of the globe is rotated away from the eye.

* Correction to commit 515167a4; need to adjust mouse position Y for use by FlyViewInputHandler, and per frame mouse/key events.

* Correct clamping of mouse position to viewport coordinates;  previous edition has used AWT size of canvas, and mouse positions from MouseEvents are converted to GL surface coordinates early on.   This commit fixes both X,Y limits, whereas commit d4b6bf43 only fixed Y.