Support disabling the GTK SessionManagerDBus via environment variables

For example this simplifies disabling the SessionManagerDBus in CI
environments where no bus is available.

Author: HannesWell

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/internal/SessionManagerDBus.java

@@ -111,7 +111,8 @@ public void remove() {
 	public SessionManagerDBus() {
 		// Allow to disable session manager, for example in case it conflicts with
 		// session manager connection implemented in application itself.
-		boolean isDisabled = System.getProperty("org.eclipse.swt.internal.SessionManagerDBus.disable") != null;
+		boolean isDisabled = System.getProperty("org.eclipse.swt.internal.SessionManagerDBus.disable") != null
+				|| System.getenv("org.eclipse.swt.internal.SessionManagerDBus.disable") != null;
 		if (isDisabled) return;
 
 		start();