Copy rectangles with APIs in DnD

This commit enforces the usage of Rectangle.copyWith and Rectangle.of
while copying a rectangle from an existing rectangle and creating a
rectangle from a Point making sure the internal state of the source
resources are copied to the new resource.

contributes to
eclipse-platform/eclipse.platform.swt#62 and
eclipse-platform/eclipse.platform.swt#128

Author: amartya4256

bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/dndaddon/DetachedDropAgent.java

@@ -94,8 +94,9 @@ public Rectangle getRectangle(MUIElement dragElement) {
 		}
 
 		Point cp = Display.getCurrent().getCursorLocation();
-		curRect.x = cp.x - 15;
-		curRect.y = cp.y - 15;
+		cp.x -= 15;
+		cp.y -= 15;
+		curRect = Rectangle.of(cp, curRect.width, curRect.height);
 
 		return curRect;
 	}

bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/dndaddon/DnDManager.java

@@ -464,8 +464,7 @@ private Rectangle getOverlayBounds() {
 		Rectangle bounds = null;
 		for (Rectangle fr : frames) {
 			if (fr.width > 6) {
-				Rectangle outerBounds = new Rectangle(fr.x - 3, fr.y - 3, fr.width + 6,
-						fr.height + 6);
+				Rectangle outerBounds = fr.copyWith(-3, -3, 6, 6);
 				if (bounds == null) {
 					bounds = outerBounds;
 				}