core_timing: Use better reference tracking for EventType. (#3159)

* core_timing: Use better reference tracking for EventType.

- Moves ownership of the event to the caller, ensuring we don't fire events for destroyed objects.
- Removes need for unique names - we won't be using this for save states anyways.

src/core/hle/service/nvflinger/nvflinger.cpp

@@ -37,8 +37,8 @@ NVFlinger::NVFlinger(Core::System& system) : system(system) {
     displays.emplace_back(4, "Null", system);
 
     // Schedule the screen composition events
-    composition_event = system.CoreTiming().RegisterEvent(
-        "ScreenComposition", [this](u64 userdata, s64 cycles_late) {
+    composition_event =
+        Core::Timing::CreateEvent("ScreenComposition", [this](u64 userdata, s64 cycles_late) {
             Compose();
             const auto ticks =
                 Settings::values.force_30fps_mode ? frame_ticks_30fps : GetNextTicks();

src/core/hle/service/nvflinger/nvflinger.h

@@ -103,7 +103,7 @@ private:
     u32 swap_interval = 1;
 
     /// Event that handles screen composition.
-    Core::Timing::EventType* composition_event;
+    std::shared_ptr<Core::Timing::EventType> composition_event;
 
     Core::System& system;
 };