doc: Fix tr() documentation issue

The declaration of tr() in the Q_OBJECT macro interferes with the
tr() declaration in the QObject class. This update fixes that bug
by resetting QT_TR_FUNCTIONS to be empty and by ensuring that the
tr() declaration in class QObject is seen by clang when qdoc is
running.

Change-Id: If55339fc417f3eee1a1e1ce3df75a18af443d630
Task-number: QTBUG-75864
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/kernel/qobject.h

@@ -117,6 +117,7 @@ public:
 class Q_CORE_EXPORT QObject
 {
     Q_OBJECT
+
     Q_PROPERTY(QString objectName READ objectName WRITE setObjectName NOTIFY objectNameChanged)
     Q_DECLARE_PRIVATE(QObject)
 
@@ -127,7 +128,7 @@ public:
     virtual bool event(QEvent *event);
     virtual bool eventFilter(QObject *watched, QEvent *event);
 
-#if defined(QT_NO_TRANSLATION)
+#if defined(QT_NO_TRANSLATION) || defined(Q_CLANG_QDOC)
     static QString tr(const char *sourceText, const char * = nullptr, int = -1)
         { return QString::fromUtf8(sourceText); }
 #if QT_DEPRECATED_SINCE(5, 0)

src/corelib/kernel/qobjectdefs.h

@@ -146,6 +146,10 @@ class QString;
 # define QT_TR_FUNCTIONS
 #endif
 
+#ifdef Q_CLANG_QDOC
+#define QT_TR_FUNCTIONS
+#endif
+
 // ### Qt6: remove
 #define Q_OBJECT_CHECK  /* empty, unused since Qt 5.2 */