[Windows] Place new windows near top-left corner of their parents #2608

If there is a parent present at the moment when the window is created
then set the initial position of the new window to be near the top-left
corner of its parent. This avoids unnecessary DPI change events in case
that the new window stays in the same monitor were its parent is.

Fixes #2608

Author: fedejeanne

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Control.java

@@ -668,12 +668,25 @@ Control computeTabRoot () {
 
 void createHandle () {
 	long hwndParent = widgetParent ();
+
+	int x=OS.CW_USEDEFAULT;
+	int y=0;
+
+	// Set it to be near the top-left corner of the parent shell by default
+	if (hwndParent != 0) {
+		RECT rect = new RECT();
+		OS.GetWindowRect(hwndParent, rect);
+
+		x = rect.left + 100;
+		y = rect.top + 100;
+	}
+
 	handle = OS.CreateWindowEx (
 		widgetExtStyle (),
 		windowClass (),
 		null,
 		widgetStyle (),
-		OS.CW_USEDEFAULT, 0, OS.CW_USEDEFAULT, 0,
+		x, y, OS.CW_USEDEFAULT, 0,
 		hwndParent,
 		0,
 		OS.GetModuleHandle (null),