QDeadlineTimer: make the ForeverConstant an enum class

Avoids the implicit cast to int, which then fixes the overloading
problem of QDeadlineTimer with older functions taking an integer with
the number of milliseconds. Without this and the workarounds, an
expression like
  waitCondition.wait(&mutex, QDeadlineTimer::Forever);
would be the same as
  waitCondition.wait(&mutex, 0);
which is the opposite of "forever".

This means we can remove the overloads added earlier this week in
commits 37f1fb78ee (QMutex),
63704529b7 (QReadWriteLock), and
37f1fb78ee (QSemaphore). I hadn't thought
this solution until noting that QWaitCondition needed the same solution
and then remembering how Qt::Uninitialized was fixed of the same
problem.

Change-Id: I5f7f427ded124479baa6fffd176023ddfb91077d
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/kernel/qdeadlinetimer.h

@@ -23,7 +23,8 @@ QT_BEGIN_NAMESPACE
 class Q_CORE_EXPORT QDeadlineTimer
 {
 public:
-    enum ForeverConstant { Forever };
+    enum class ForeverConstant { Forever };
+    static constexpr ForeverConstant Forever = ForeverConstant::Forever;
 
     constexpr QDeadlineTimer(Qt::TimerType type_ = Qt::CoarseTimer) noexcept
         : type(type_) {}

src/corelib/thread/qmutex.h

@@ -145,12 +145,6 @@ public:
         return success;
     }
 
-#ifndef Q_QDOC
-    // because tryLock(QDeadlineTimer::Forever) is tryLock(0)
-    bool tryLock(QDeadlineTimer::ForeverConstant) QT_MUTEX_LOCK_NOEXCEPT
-    { lock(); return true; }
-#endif
-
     // TimedLockable concept
     template <class Rep, class Period>
     bool try_lock_for(std::chrono::duration<Rep, Period> duration)

src/corelib/thread/qreadwritelock.h

@@ -43,15 +43,6 @@ public:
 
     void unlock();
 
-#ifndef Q_QDOC
-    // because tryLockForXxx(QDeadlineTimer::Forever) is the same
-    // as tryLockForXxx(0), which is not forever
-    bool tryLockForRead(QDeadlineTimer::ForeverConstant)
-    { lockForRead(); return true; }
-    bool tryLockForWrite(QDeadlineTimer::ForeverConstant)
-    { lockForWrite(); return true; }
-#endif
-
 private:
     Q_DISABLE_COPY(QReadWriteLock)
     QAtomicPointer<QReadWriteLockPrivate> d_ptr;

src/corelib/thread/qsemaphore.h

@@ -23,11 +23,6 @@ public:
     QT_CORE_INLINE_SINCE(6, 6)
     bool tryAcquire(int n, int timeout);
     bool tryAcquire(int n, QDeadlineTimer timeout);
-#ifndef Q_QDOC
-    // because tryAcquire(n, QDeadlineTimer::Forever) is tryLock(n, 0)
-    bool tryAcquire(int n, QDeadlineTimer::ForeverConstant)
-    { acquire(n); return true; }
-#endif
 #if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
     template <typename Rep, typename Period>
     bool tryAcquire(int n, std::chrono::duration<Rep, Period> timeout)