JNI: add swap to QJniArray

It's a value type and should implement swap.

Change-Id: I811377843b6ede1d6d750a701ae7a6b12434f4e6
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
(cherry picked from commit 0789dd8723b03d255ff203c717c5e12b6945015e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qjniarray.h

@@ -237,6 +237,8 @@ protected:
     template <typename List>
     static auto makeObjectArray(List &&list);
 
+    void swap(QJniArrayBase &other) noexcept { m_object.swap(other.m_object); }
+
 private:
     QJniObject m_object;
 };

src/corelib/kernel/qjniarray.qdoc

@@ -58,6 +58,12 @@
     \return a QJniObject wrapping the same \c{jobject} as this QJniArray instance.
 */
 
+/*!
+    \fn void QJniArrayBase::swap(QJniArrayBase &other)
+
+    Swaps this array object with \a other. This function is very fast and never fails.
+*/
+
 /*!
     \fn template <typename T> T QJniArrayBase::object() const