Initialize Win32 Display thread with correct OS DPI awareness

The runtime auto-scaling for multi-monitor HiDPI support on Windows
requires the system's DPI awareness to be set to PerMonitorV2. This
change makes the Display class initialize its UI thread with the
according DPI awareness.

Contributes to
#62
Contributes to
#131

Author: HeikoKlare

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

@@ -582,6 +582,29 @@ public Display () {
  */
 public Display (DeviceData data) {
 	super (data);
+	initializeProperDPIAwareness();
+}
+
+private void initializeProperDPIAwareness() {
+	if (!DPIUtil.isAutoScaleOnRuntimeActive()) {
+		return;
+	}
+	// Auto scaling on runtime requires DPI awareness mode "Per Monitor V2"
+	boolean perMonitorV2Available = OS.WIN32_BUILD > OS.WIN32_BUILD_WIN10_1809;
+	if (!perMonitorV2Available) {
+		System.err.println(
+				"***WARNING: rescaling at runtime is activated but the OS version does not support required DPI awareness mode PerMonitorV2.");
+		return;
+	}
+
+	boolean alreadyUsesPerMonitorV2 = OS.GetThreadDpiAwarenessContext() == OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2;
+	if (alreadyUsesPerMonitorV2) {
+		return;
+	}
+	long setDpiAwarenessResult = OS.SetThreadDpiAwarenessContext(OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
+	if (setDpiAwarenessResult == 0L) {
+		System.err.println("***WARNING: setting DPI awareness to PerMonitorV2 failed.");
+	}
 }
 
 Control _getFocusControl () {