Frontend/GPU: Refactor context management

Changes the GraphicsContext to be managed by the GPU core. This
eliminates the need for the frontends to fool around with tricky
MakeCurrent/DoneCurrent calls that are dependent on the settings (such
as async gpu option).

This also refactors out the need to use QWidget::fromWindowContainer as
that caused issues with focus and input handling. Now we use a regular
QWidget and just access the native windowHandle() directly.

Another change is removing the debug tool setting in FrameMailbox.
Instead of trying to block the frontend until a new frame is ready, the
core will now take over presentation and draw directly to the window if
the renderer detects that its hooked by NSight or RenderDoc

Lastly, since it was in the way, I removed ScopeAcquireWindowContext and
replaced it with a simple subclass in GraphicsContext that achieves the
same result

src/core/frontend/emu_window.h

@@ -13,19 +13,39 @@
 namespace Core::Frontend {
 
 /**
- * Represents a graphics context that can be used for background computation or drawing. If the
- * graphics backend doesn't require the context, then the implementation of these methods can be
- * stubs
+ * Represents a drawing context that supports graphics operations.
  */
 class GraphicsContext {
 public:
     virtual ~GraphicsContext();
 
+    /// Inform the driver to swap the front/back buffers and present the current image
+    virtual void SwapBuffers() {}
+
     /// Makes the graphics context current for the caller thread
-    virtual void MakeCurrent() = 0;
+    virtual void MakeCurrent() {}
 
     /// Releases (dunno if this is the "right" word) the context from the caller thread
-    virtual void DoneCurrent() = 0;
+    virtual void DoneCurrent() {}
+
+    class Scoped {
+    public:
+        Scoped(GraphicsContext& context_) : context(context_) {
+            context.MakeCurrent();
+        }
+        ~Scoped() {
+            context.DoneCurrent();
+        }
+
+    private:
+        GraphicsContext& context;
+    };
+
+    /// Calls MakeCurrent on the context and calls DoneCurrent when the scope for the returned value
+    /// ends
+    Scoped Acquire() {
+        return Scoped{*this};
+    }
 };
 
 /**
@@ -46,7 +66,7 @@ public:
  * - DO NOT TREAT THIS CLASS AS A GUI TOOLKIT ABSTRACTION LAYER. That's not what it is. Please
  *   re-read the upper points again and think about it if you don't see this.
  */
-class EmuWindow : public GraphicsContext {
+class EmuWindow {
 public:
     /// Data structure to store emuwindow configuration
     struct WindowConfig {
@@ -60,17 +80,9 @@ public:
     virtual void PollEvents() = 0;
 
     /**
-     * Returns a GraphicsContext that the frontend provides that is shared with the emu window. This
-     * context can be used from other threads for background graphics computation. If the frontend
-     * is using a graphics backend that doesn't need anything specific to run on a different thread,
-     * then it can use a stubbed implemenation for GraphicsContext.
-     *
-     * If the return value is null, then the core should assume that the frontend cannot provide a
-     * Shared Context
+     * Returns a GraphicsContext that the frontend provides to be used for rendering.
      */
-    virtual std::unique_ptr<GraphicsContext> CreateSharedContext() const {
-        return nullptr;
-    }
+    virtual std::unique_ptr<GraphicsContext> CreateSharedContext() const = 0;
 
     /// Returns if window is shown (not minimized)
     virtual bool IsShown() const = 0;