Android: enable tst_QScreen::grabWindow

Two things are done here:
- use showNormal() instead of show() to get an expected widget size.
- skip the test if HighDPI scaling is enabled with non-integer scaling
  factor, because there can be rounding errors.

Fixes: QTBUG-87390
Pick-to: 6.3 6.2
Change-Id: I653a17bac2142838b03a328e1629582384b6c7b3
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

tests/auto/gui/kernel/qscreen/BLACKLIST

@@ -1,5 +1,3 @@
-# QTBUG-87390
 [grabWindow]
-android
 # QTBUG-100412
 windows

tests/auto/gui/kernel/qscreen/tst_qscreen.cpp

@@ -32,6 +32,7 @@
 #include <qpa/qwindowsysteminterface.h>
 #include <qpa/qplatformintegration.h>
 #include <private/qguiapplication_p.h>
+#include <private/qhighdpiscaling_p.h>
 
 #include <QTest>
 #include <QSignalSpy>
@@ -282,9 +283,20 @@ void tst_QScreen::grabWindow()
     QCOMPARE(screen->name().toUtf8(), screenName);
     const double screenDpr = screen->devicePixelRatio();
 
+    if (QHighDpiScaling::isActive()) {
+        const float rawFactor = QHighDpiScaling::factor(screen);
+        const float roundedFactor = qRound(rawFactor);
+        if (!qFuzzyCompare(roundedFactor, rawFactor))
+            QSKIP("HighDPI enabled with non-integer factor. Skip due to possible rounding errors.");
+    }
+
     Window window(screen);
     window.setGeometry(windowRect);
+#ifndef Q_OS_ANDROID
     window.show();
+#else
+    window.showNormal();
+#endif
 
     if (!QTest::qWaitForWindowExposed(&window))
         QSKIP("Failed to expose window - aborting");