Add missing QString::prepend(QStringRef)/(const QChar*,int) overloads

QString::append(QStringRef) exists, and so should prepend().
QString::append(const QChar *,int) exists, and so should prepend().

[ChangeLog][QtCore][QString] Added prepend(QStringRef) and prepent(const QChar *, int) overloads.

Change-Id: I3eca41045f7c481be473507e23e92690f3ed7ba3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@theqtcompany.com>

src/corelib/tools/qstring.cpp

@@ -2072,6 +2072,22 @@ QString &QString::append(QChar ch)
     Prepends the Latin-1 string \a str to this string.
 */
 
+/*! \fn QString &QString::prepend(const QChar *str, int len)
+    \since 5.5
+    \overload prepend()
+
+    Prepends \a len characters from the QChar array \a str to this string and
+    returns a reference to this string.
+*/
+
+/*! \fn QString &QString::prepend(const QStringRef &str)
+    \since 5.5
+    \overload prepend()
+
+    Prepends the string reference \a str to the beginning of this string and
+    returns a reference to this string.
+*/
+
 /*! \fn QString &QString::prepend(const QByteArray &ba)
 
     \overload prepend()

src/corelib/tools/qstring.h

@@ -428,7 +428,9 @@ public:
     QString &append(const QStringRef &s);
     QString &append(QLatin1String s);
     inline QString &prepend(QChar c) { return insert(0, c); }
+    inline QString &prepend(const QChar *uc, int len) { return insert(0, uc, len); }
     inline QString &prepend(const QString &s) { return insert(0, s); }
+    inline QString &prepend(const QStringRef &s) { return insert(0, s); }
     inline QString &prepend(QLatin1String s) { return insert(0, s); }
 
     inline QString &operator+=(QChar c) {

tests/auto/corelib/tools/qstring/tst_qstring.cpp

@@ -375,8 +375,12 @@ private slots:
 
     void prepend_qstring()            { prepend_impl<QString>(); }
     void prepend_qstring_data()       { prepend_data(true); }
+    void prepend_qstringref()         { prepend_impl<QStringRef>(); }
+    void prepend_qstringref_data()    { prepend_data(true); }
     void prepend_qlatin1string()      { prepend_impl<QLatin1String, QString &(QString::*)(QLatin1String)>(); }
     void prepend_qlatin1string_data() { prepend_data(true); }
+    void prepend_qcharstar_int()      { prepend_impl<QPair<const QChar *, int>, QString &(QString::*)(const QChar *, int)>(); }
+    void prepend_qcharstar_int_data() { prepend_data(true); }
     void prepend_qchar()              { prepend_impl<Reversed<QChar>, QString &(QString::*)(QChar)>(); }
     void prepend_qchar_data()         { prepend_data(true); }
     void prepend_qbytearray()         { prepend_impl<QByteArray>(); }