Dear ImGui Implementation (#598)

* added imgui as dependency

* imgui renderer/basic input implementation

* imgui: add layers system

Add video info layer to show fps. Press F10 to toggle it.

* imgui: add custom imgui config

* imgui: gamepad capture, stopping propagation

* imgui: changed config & log file path to use portable dir

* videoout: render blank frame when video output is closed

required to render imgui even when game has no video output

- fixed merge compile-error

src/imgui/imgui_layer.h

@@ -0,0 +1,21 @@
+// SPDX-FileCopyrightText: Copyright 2024 shadPS4 Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+namespace ImGui {
+
+class Layer {
+public:
+    virtual ~Layer() = default;
+    static void AddLayer(Layer* layer);
+    static void RemoveLayer(Layer* layer);
+
+    virtual void Draw() = 0;
+
+    virtual bool ShouldGrabGamepad() {
+        return false;
+    }
+};
+
+} // namespace ImGui