[desktop] More qt_common reorganization (#3916)

Ported from QML branch.

Main "big" change is that EmuThread is now a shared state in QtCommon,
not individually managed/passed around by GRenderWindow and MainWindow.

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3916
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

src/common/settings.cpp

@@ -435,4 +435,16 @@ void ToggleSlowMode() {
         SetSpeedMode(SpeedMode::Standard);
 }
 
+bool IsOpenGL() {
+    const auto backend = Settings::values.renderer_backend.GetValue();
+    switch (backend) {
+    case RendererBackend::OpenGL_GLSL:
+    case RendererBackend::OpenGL_GLASM:
+    case RendererBackend::OpenGL_SPIRV:
+        return true;
+    default:
+        return false;
+    }
+}
+
 } // namespace Settings