QFlags: add (named) explicit conversion from/to int

There are some use cases where one may want to convert a QFlags object
from/to an integer deliberately; for instance, to store it in a
bitfield, saving some space. So far this worked by means of a implicit
conversions; instead, also add named conversions for this.

[ChangeLog][QtCore][QFlags] Added the fromInt() and toInt() functions
for explicit conversions from/to a plain integer.

Change-Id: I705559bf75b28c30b4446bb6d0753aedfc808eed
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qflags.h

@@ -112,6 +112,9 @@ public:
     constexpr inline QFlags(std::initializer_list<Enum> flags) noexcept
         : i(initializer_list_helper(flags.begin(), flags.end())) {}
 
+    constexpr static inline QFlags fromInt(Int i) noexcept { return QFlags(QFlag(i)); }
+    constexpr inline Int toInt() const noexcept { return i; }
+
     constexpr inline QFlags &operator&=(int mask) noexcept { i &= mask; return *this; }
     constexpr inline QFlags &operator&=(uint mask) noexcept { i &= mask; return *this; }
     constexpr inline QFlags &operator&=(Enum mask) noexcept { i &= Int(mask); return *this; }

src/corelib/global/qglobal.cpp

@@ -497,6 +497,24 @@ static_assert(sizeof(qint64) == 8, "Internal error, qint64 is misdefined");
     \a on is \c false. Returns a reference to this object.
 */
 
+/*!
+    \fn template <typename Enum> QFlags<Enum> QFlags<Enum>::fromInt(Int i) noexcept
+    \since 6.2
+
+    Constructs a QFlags object representing the integer value \a i.
+*/
+
+/*!
+    \fn template <typename Enum> Int QFlags<Enum>::toInt() const noexcept
+    \since 6.2
+
+    Returns the value stored in the QFlags object as an integer. Note
+    that the returned integer may be signed or unsigned, depending on
+    whether the enum's underlying type is signed or unsigned.
+
+    \sa Int
+*/
+
 /*!
   \macro Q_DISABLE_COPY(Class)
   \relates QObject