The KGlobalAccelD which gets created by KWin needs a plugin for the
platform specific parts. This change introduces such a plugin. It's
linked against kwin so that it can integrate with the core.
On enable the plugin registers itself in the InputRedirection and
GlobalShortcutsManager checks the plugin whether a shortcut got
triggered.
As the loading of the plugin must happen after InputRedirection is
fully created a dedicated init method is added to InputRedirection.
REVIEW: 124187
