Doc: Properly document old platform-specific functions

qt_mac_set_dock_menu() needs a \relates command to show up properly.
"\since 5.2" produces "This function was introduced in Qt 5.2", which is
wrong; the function existed in Qt 4.

qt_set_sequence_auto_mnemonic() is referenced by the QShortcut class
ref, but the page that hosted it in qtdoc.git is being removed. Thus,
its description is now transferred here.

Change-Id: If009a45f1d04541787925cf230ed7b59c7db0b39
Reviewed-by: Alejandro Exojo Piqueras <suy@badopi.org>
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

src/gui/kernel/qkeysequence.cpp

@@ -140,6 +140,23 @@ static int qtkeyForMacSymbol(const QChar ch)
 #else
 static bool qt_sequence_no_mnemonics = false;
 #endif
+
+/*!
+    \fn void qt_set_sequence_auto_mnemonic(bool b)
+    \relates QKeySequence
+
+    Specifies whether mnemonics for menu items, labels, etc., should
+    be honored or not. On Windows and X11, this feature is
+    on by default; on OS X, it is off. When this feature is off
+    (that is, when \a b is false), QKeySequence::mnemonic() always
+    returns an empty string.
+
+    \note This function is not declared in any of Qt's header files.
+    To use it in your application, declare the function prototype
+    before calling it.
+
+    \sa QShortcut
+*/
 void Q_GUI_EXPORT qt_set_sequence_auto_mnemonic(bool b) { qt_sequence_no_mnemonics = !b; }
 
 /*!

src/widgets/kernel/qshortcut.cpp

@@ -329,7 +329,7 @@ static bool correctActionContext(Qt::ShortcutContext context, QAction *a, QWidge
     shown and the character will be underlined. On Windows, shortcuts
     are normally not displayed until the user presses the \uicontrol Alt
     key, but this is a setting the user can change. On Mac, shortcuts
-    are disabled by default. Call qt_set_sequence_auto_mnemonic() to
+    are disabled by default. Call \l qt_set_sequence_auto_mnemonic() to
     enable them. However, because mnemonic shortcuts do not fit in
     with Aqua's guidelines, Qt will not show the shortcut character
     underlined.

src/widgets/widgets/qmenu_mac.mm

@@ -98,15 +98,13 @@ void QMenu::setAsDockMenu()
 
 
 /*! \fn void qt_mac_set_dock_menu(QMenu *menu)
-    \since 5.2
+    \relates QMenu
     \deprecated
 
-    Set this menu to be the dock menu available by option-clicking
+    Sets this \a menu to be the dock menu available by option-clicking
     on the application dock icon. Available on OS X only.
 
-    Deprecated; use QMenu:setAsDockMenu() instead.
-
-    \sa QMenu:setAsDockMenu()
+    Deprecated; use \l QMenu::setAsDockMenu() instead.
 */
 
 void QMenuPrivate::moveWidgetToPlatformItem(QWidget *widget, QPlatformMenuItem* item)