Adding readAndDispatch() in drawImage test to make the test not flaky

The reasoning to add readAndDispatch() is to consider the case when e.gc.drawImage()'s draw request to the OS, might not have completed by the time gcCopy.copyArea() was called. Using readAndDispatch() is to ensure all OS events are processed, so there’s no pending work left.

Author: arunjose696

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_GC.java

@@ -279,6 +279,8 @@ public boolean isAutoScalable() {
     });
 
     shell.open();
+    while (display.readAndDispatch()) {
+    }
     Image target = new Image(display, canvasWidth, canvasHeight);
     GC gcCopy = new GC(canvas);
     gcCopy.copyArea(target, 0, 0);