Doc: Document QApplicationStatic convenience header

Task-number: QTBUG-125097
Change-Id: Ib71dfe7696fb50759e43b0c8dee70860f1837d9b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 197a1f1a7716c9ddbdf9c458686bafa740f726cd)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/global/qglobal.cpp

@@ -63,6 +63,7 @@ using namespace Qt::StringLiterals;
     \row    \li <QFlags>                    \li Type-safe way of combining enum values
     \row    \li \l <QForeach>               \li Qt's implementation of foreach and forever loops
     \row    \li \l <QFunctionPointer>       \li Typedef for a pointer-to-function type
+    \row    \li \l <QApplicationStatic>     \li For Q_APPLICATION_STATIC
     \row    \li <QGlobalStatic>             \li Thread-safe initialization of global static objects
     \row    \li \l <QOverload>              \li Helpers for resolving member function overloads
     \row    \li <QSysInfo>                  \li A helper class to get system information

src/corelib/kernel/qapplicationstatic.qdoc

@@ -1,10 +1,15 @@
 // Copyright (C) 2021 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
+/*!
+    \headerfile <QApplicationStatic>
+    \inmodule QtCore
+*/
+
 /*!
     \macro Q_APPLICATION_STATIC(Type, VariableName, ...)
     \since 6.3
-    \relates QGlobalStatic
+    \relates <QApplicationStatic>
 
     This macro extends Q_GLOBAL_STATIC and creates a global and static object
     of type \l QGlobalStatic, of name \a VariableName, initialized by the