dispatchers: add forceidle (#11922)

The forceidle dispatcher resets all ext-idle-notify timers as if the
user had been idle for the specified number of seconds. If a
notification has already fired, but would now be set with a nonzero
delay, then it is reset. Conversely, if a timer has not yet fired, but
would now be set to a nonpositive delay, then it is immediately fired.
This process ignores any existing inhibitors, but timers are otherwise
reset as normal if any new inhibitors are created or destroyed.

src/managers/KeybindManager.hpp

@@ -237,6 +237,7 @@ class CKeybindManager {
     static SDispatchResult global(std::string);
     static SDispatchResult event(std::string);
     static SDispatchResult setProp(std::string);
+    static SDispatchResult forceIdle(std::string);
 
     friend class CCompositor;
     friend class CInputManager;