Don't show mnemonics in dockwidget titles

One might want to add an accellerator to dockwidget titles to be used in
contexts that isn't directly the title, but still uses the title.

Dockwidget title accelerators doesn't work in dock widgets, so don't
show them.

They are still available in e.g. a right click menu on a dockwidget to
hide/show, and here the accellerator might come handy, and also if a
dockwidget is tabbed.

Pick-to: 6.6 6.7
Change-Id: I196e1aa92a5c53fed735b598653c267509f788b8
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>

src/widgets/styles/qcommonstyle.cpp

@@ -2175,7 +2175,7 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
 
                 const int indent = p->fontMetrics().descent();
                 proxy()->drawItemText(p, r.adjusted(indent + 1, 1, -indent - 1, -1),
-                              Qt::AlignLeft | Qt::AlignVCenter, dwOpt->palette,
+                              Qt::AlignLeft | Qt::AlignVCenter | Qt::TextHideMnemonic, dwOpt->palette,
                               dwOpt->state & State_Enabled, dwOpt->title,
                               QPalette::WindowText);
             }

src/widgets/styles/qfusionstyle.cpp

@@ -1134,7 +1134,7 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
                                                             Qt::ElideRight, titleRect.width());
                 proxy()->drawItemText(painter,
                                       titleRect,
-                                      Qt::AlignLeft | Qt::AlignVCenter, dwOpt->palette,
+                                      Qt::AlignLeft | Qt::AlignVCenter | Qt::TextHideMnemonic, dwOpt->palette,
                                       dwOpt->state & State_Enabled, titleText,
                                       QPalette::WindowText);
             }

src/widgets/styles/qwindowsstyle.cpp

@@ -1777,7 +1777,7 @@ void QWindowsStyle::drawControl(ControlElement ce, const QStyleOption *opt, QPai
                                     titleRect.height(), titleRect.width());
                 }
                 proxy()->drawItemText(p, titleRect,
-                            Qt::AlignLeft | Qt::AlignVCenter, palette,
+                            Qt::AlignLeft | Qt::AlignVCenter | Qt::TextHideMnemonic, palette,
                             dwOpt->state & State_Enabled, dwOpt->title,
                             floating ? (active ? QPalette::BrightText : QPalette::Window) : QPalette::WindowText);
                 p->setFont(oldFont);