Use new "Show/Hide Hidden Files" standard shortcut

Summary:
Note that we lose the F8 shortcut since the KStandardShortcut added in XXXX can only
accommodate toew default shortcuts, and I thought Ctrl+H and Alt+. were the more important
ones. Hopefully that's not too high a price to pay.

Depends on D28802

Test Plan:
- Apply D28802 to kconfig
- Apply this patch to Dolphin, compile, and launch Dolphin
- Hit Ctrl+H or Alt+. and see that hidden files are shown or hidden as approproiate

Reviewers: #dolphin, dfaure, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D28804

src/views/dolphinviewactionhandler.cpp

@@ -283,7 +283,7 @@ void DolphinViewActionHandler::createActions()
         "<para>Hidden items only differ from other ones in that their "
         "name starts with a \".\". In general there is no need for "
         "users to access them which is why they are hidden.</para>"));
-    m_actionCollection->setDefaultShortcuts(showHiddenFiles, {Qt::ALT + Qt::Key_Period, Qt::CTRL + Qt::Key_H, Qt::Key_F8});
+    m_actionCollection->setDefaultShortcuts(showHiddenFiles, KStandardShortcut::showHideHiddenFiles());
     connect(showHiddenFiles, &KToggleAction::triggered, this, &DolphinViewActionHandler::toggleShowHiddenFiles);
 
     QAction* adjustViewProps = m_actionCollection->addAction(QStringLiteral("view_properties"));