Kernel/Interrupts: Enumerate nested handlers in a shared handler

When asked to enumerate all interrupt handlers, display all shared
handlers within it instead of just returning the responsible handler of
them.

Kernel/Interrupts/SharedIRQHandler.h

@@ -26,6 +26,8 @@ public:
 
     virtual bool eoi() override;
 
+    void enumerate_handlers(Function<void(GenericInterruptHandler&)>&);
+
     virtual size_t sharing_devices_count() const override { return m_handlers.size(); }
     virtual bool is_shared_handler() const override { return true; }
     virtual bool is_sharing_with_others() const override { return false; }