Introduce an Event system to VideoCommon

A lot of the remaining complexity in Renderer is the massive Swap function
which tries to handle a bunch of FrameBegin/FrameEnd events.

Rather than create a new place for it. This event system will try
to distribute it all over the place

Source/Core/VideoCommon/VideoEvents.h

@@ -0,0 +1,84 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/CommonTypes.h"
+#include "Common/EventHook.h"
+
+
+// Called when certain video config setting are changed
+using ConfigChangedEvent = Event<"ConfigChanged", u32>;
+
+// An event called just before the first draw call of a frame
+using BeforeFrameEvent = Event<"BeforeFrame">;
+
+// An event called after the frame XFB copy begins processing on the host GPU.
+// Useful for "once per frame" usecases.
+// Note: In a few rare cases, games do multiple XFB copies per frame and join them while presenting.
+//       If this matters to your usecase, you should use BeforePresent instead.
+using AfterFrameEvent = Event<"AfterFrame">;
+
+struct PresentInfo
+{
+    enum class PresentReason
+    {
+      Immediate, // FIFO is Presenting the XFB immediately, straight after the XFB copy
+      VideoInterface, // VideoInterface has triggered a present with a new frame
+      VideoInterfaceDuplicate, // VideoInterface has triggered a present with a duplicate frame
+    };
+
+    // The number of (unique) frames since the emulated console booted
+    u64 frame_count;
+
+
+    // The number of presents since the video backend was initialized.
+    // never goes backwards.
+    u64 present_count;
+
+    // The frame is identical to the previous frame
+    PresentReason reason;
+
+    // The exact emulated time of the when real hardware would have presented this frame
+    // FIXME: Immediate should predict the timestamp of this present
+     u64 emulated_timestamp;
+
+    // TODO:
+    // u64 intended_present_time;
+
+    // AfterPresent only: The actual time the frame was presented
+    u64 actual_present_time = 0;
+
+    enum class PresentTimeAccuracy
+    {
+        // The Driver/OS has given us an exact timestamp of when the first line of the frame started
+        // scanning out to the monitor
+        PresentOnScreenExact,
+
+        // An approximate timestamp of scanout.
+        PresentOnScreen,
+
+        // Dolphin doesn't have visibility of the present time. But the present operation has
+        // been queued with the GPU driver and will happen in the near future.
+        PresentInProgress,
+
+        // Not implemented
+        Unimplemented,
+    };
+
+    // Accuracy of actual_present_time
+    PresentTimeAccuracy present_time_accuracy = PresentTimeAccuracy::Unimplemented;
+};
+
+// An event called just as a frame is queued for presentation.
+// The exact timing of this event depends on the "Immediately Present XFB" option.
+//
+// If enabled, this event will trigger immediately after AfterFrame
+// If disabled, this event won't trigger until the emulated interface starts drawing out a new frame.
+//
+// frame_count: The number of frames
+using BeforePresentEvent = Event<"BeforePresent", PresentInfo&>;
+
+// An event that is triggered after a frame is presented.
+// The exact timing of this event depends on backend/driver support.
+using AfterPresentEvent = Event<"AfterPresent", PresentInfo&>;