LibCore: Add Core::Timer::set_active(bool)

This calls either start() or stop() depending on the boolean argument.

Userland/Libraries/LibCore/Timer.cpp

@@ -58,6 +58,14 @@ void Timer::stop()
     m_active = false;
 }
 
+void Timer::set_active(bool active)
+{
+    if (active)
+        start();
+    else
+        stop();
+}
+
 void Timer::timer_event(TimerEvent&)
 {
     if (m_single_shot)

Userland/Libraries/LibCore/Timer.h

@@ -37,6 +37,8 @@ public:
     void restart(int interval_ms);
     void stop();
 
+    void set_active(bool);
+
     bool is_active() const { return m_active; }
     int interval() const { return m_interval_ms; }
     void set_interval(int interval_ms)