fix(wlr/taskbar): dispatch built-in click actions via doAction, not the shell

wlr/taskbar reads on-click* config values (close, minimize, maximize,
fullscreen, minimize-raise, activate) directly as internal actions in
Task::handle_clicked, but never adopted the eventActionMap_/doAction
mechanism. As a result AModule::handleUserEvent additionally forkExec-ed
the same value as a shell command, e.g. on-click-middle: "close" ran the
action and then failed with "sh: line 1: close: command not found".

Register the taskbar built-in action names in eventActionMap_ so they are
recognized as module actions, and skip the shell forkExec in
handleUserEvent when the configured value is a recognized module action.
Non-action values are still run as user shell commands.

Fixes #3284.

include/AModule.hpp

@@ -98,6 +98,13 @@ class AModule : public IModule {
   bool disable_on_sleep_{false};
   GObject* menu_ = nullptr;
 
+  // Maps a configured event name (e.g. "on-click-middle") to a built-in module
+  // action name. Populated from the `actions` config section, and by modules
+  // that interpret on-click* config values as internal actions (e.g.
+  // wlr/taskbar). Entries here are dispatched through doAction() instead of
+  // being run as shell commands.
+  std::map<std::string, std::string> eventActionMap_;
+
  private:
   bool handleUserEvent(GdkEventButton* const& ev);
   const bool isTooltip;
@@ -106,7 +113,6 @@ class AModule : public IModule {
   gdouble distance_scrolled_y_;
   gdouble distance_scrolled_x_;
   sigc::connection cursor_timeout_conn_;
-  std::map<std::string, std::string> eventActionMap_;
   static const inline std::map<std::pair<uint, GdkEventType>, std::string> eventMap_{
       {std::make_pair(1, GdkEventType::GDK_BUTTON_PRESS), "on-click"},
       {std::make_pair(1, GdkEventType::GDK_BUTTON_RELEASE), "on-click-release"},