QFlags: add qHash overload

Stop going through the implicit int conversion.

[ChangeLog][QtCore][QFlags] QFlags now has a qHash() overload.

Change-Id: Id380ed252695f24af2e8c239b650dcb6f44e2893
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qglobal.cpp

@@ -515,6 +515,15 @@ static_assert(sizeof(qint64) == 8, "Internal error, qint64 is misdefined");
     \sa Int
 */
 
+/*!
+    \fn template <typename Enum> size_t qHash(QFlags<Enum> flags, size_t seed = 0) noexcept
+    \since 6.2
+    \relates QFlags
+
+    Calculates the hash for the flags \a flags, using \a seed
+    to seed the calcualtion.
+*/
+
 /*!
   \macro Q_DISABLE_COPY(Class)
   \relates QObject

src/corelib/tools/qhashfunctions.h

@@ -175,6 +175,10 @@ Q_DECL_CONST_FUNCTION constexpr inline size_t qHash(QKeyCombination key, size_t
 { return qHash(key.toCombined(), seed); }
 Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qt_hash(QStringView key, uint chained = 0) noexcept;
 
+template <typename Enum>
+Q_DECL_CONST_FUNCTION constexpr inline size_t qHash(QFlags<Enum> flags, size_t seed = 0) noexcept
+{ return qHash(flags.toInt(), seed); }
+
 template <typename T, std::enable_if_t<QHashPrivate::HasQHashSingleArgOverload<T>, bool> = true>
 size_t qHash(const T &t, size_t seed) noexcept(noexcept(qHash(t)))
 { return qHash(t) ^ seed; }