Add API to get the Android API level

The Android SDK version, or API level, is commonly used to determine
what APIs are available at runtime.

[ChangeLog][QtAndroidExtras] Added convenience method for getting the
Android SDK version.

Change-Id: Ic20322f68bc9680aec9e1c8404583462063904db
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

src/androidextras/android/qandroidfunctions.cpp

@@ -66,4 +66,15 @@ QAndroidJniObject QtAndroid::androidActivity()
     return QtAndroidPrivate::activity();
 }
 
+/*!
+    \since 5.3
+    \fn int QtAndroid::androidSdkVersion()
+
+    Returns the Android SDK version. This is also known as the API level.
+*/
+int QtAndroid::androidSdkVersion()
+{
+    return QtAndroidPrivate::androidSdkVersion();
+}
+
 QT_END_NAMESPACE

src/androidextras/android/qandroidfunctions.h

@@ -54,6 +54,7 @@ QT_BEGIN_NAMESPACE
 namespace QtAndroid
 {
     Q_ANDROIDEXTRAS_EXPORT QAndroidJniObject androidActivity();
+    Q_ANDROIDEXTRAS_EXPORT int androidSdkVersion();
 }
 
 QT_END_NAMESPACE

tests/auto/qandroidfunctions/tst_qandroidfunctions.cpp

@@ -46,9 +46,15 @@ class tst_QAndroidFunctions : public QObject
 {
     Q_OBJECT
 private slots:
+    void testAndroidSdkVersion();
     void testAndroidActivity();
 };
 
+void tst_QAndroidFunctions::testAndroidSdkVersion()
+{
+    QVERIFY(QtAndroid::androidSdkVersion() > 0);
+}
+
 void tst_QAndroidFunctions::testAndroidActivity()
 {
     QAndroidJniObject activity = QtAndroid::androidActivity();