QLatin1String: add toString()

For symmetry with other views.

[ChangeLog][QtCore][QLatin1String] Added toString().

Change-Id: I4a0677e2dbd009e8da097f4cb0dbb27a6baf5469
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/text/qstring.cpp

@@ -9098,6 +9098,16 @@ QString &QString::setRawData(const QChar *unicode, int size)
     \sa latin1()
 */
 
+/*!
+    \fn QLatin1String::toString() const
+    \since 6.0
+
+    Converts this Latin-1 string into a QString. Equivalent to
+    \code
+    return QString(*this);
+    \endcode
+*/
+
 /*! \fn const char *QLatin1String::latin1() const
 
     Returns the Latin-1 string stored in this object.

src/corelib/text/qstring.h

@@ -93,6 +93,8 @@ public:
     Q_DECL_CONSTEXPR inline explicit QLatin1String(const char *s, int sz) noexcept : m_size(sz), m_data(s) {}
     inline explicit QLatin1String(const QByteArray &s) noexcept : m_size(int(qstrnlen(s.constData(), s.size()))), m_data(s.constData()) {}
 
+    inline QString toString() const;
+
     Q_DECL_CONSTEXPR const char *latin1() const noexcept { return m_data; }
     Q_DECL_CONSTEXPR int size() const noexcept { return m_size; }
     Q_DECL_CONSTEXPR const char *data() const noexcept { return m_data; }
@@ -1057,6 +1059,12 @@ public:
     inline DataPointer &data_ptr() { return d; }
 };
 
+//
+// QLatin1String inline members that require QString:
+//
+
+QString QLatin1String::toString() const { return *this; }
+
 //
 // QStringView inline members that require QString:
 //