main: Enable High DPI fixes for Qt >= 5.14

This uses Qt's new high DPI application attributes for scaling the current window.
However, these aren't perfect as scaling with non integer scales will cause artifacts in UI, icons and other elements.
Therefore, we use a heuristic to select an appropriate integer scale value depending on the current screen resolution and applies this to the application.

src/yuzu/main.cpp

@@ -4400,6 +4400,46 @@ void GMainWindow::changeEvent(QEvent* event) {
 #undef main
 #endif
 
+static void SetHighDPIAttributes() {
+    // Create a temporary QApplication.
+    int temp_argc = 0;
+    char** temp_argv = nullptr;
+    QApplication temp{temp_argc, temp_argv};
+
+    // Get the current screen geometry.
+    const QScreen* primary_screen = QGuiApplication::primaryScreen();
+    if (primary_screen == nullptr) {
+        return;
+    }
+
+    const QRect screen_rect = primary_screen->geometry();
+    const int real_width = screen_rect.width();
+    const int real_height = screen_rect.height();
+    const float real_ratio = primary_screen->logicalDotsPerInch() / 96.0f;
+
+    // Recommended minimum width and height for proper window fit.
+    // Any screen with a lower resolution than this will still have a scale of 1.
+    constexpr float minimum_width = 1350.0f;
+    constexpr float minimum_height = 900.0f;
+
+    const float width_ratio = std::max(1.0f, real_width / minimum_width);
+    const float height_ratio = std::max(1.0f, real_height / minimum_height);
+
+    // Get the lower of the 2 ratios and truncate, this is the maximum integer scale.
+    const float max_ratio = std::trunc(std::min(width_ratio, height_ratio));
+
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+
+    if (max_ratio > real_ratio) {
+        QApplication::setHighDpiScaleFactorRoundingPolicy(
+            Qt::HighDpiScaleFactorRoundingPolicy::Round);
+    } else {
+        QApplication::setHighDpiScaleFactorRoundingPolicy(
+            Qt::HighDpiScaleFactorRoundingPolicy::Floor);
+    }
+}
+
 int main(int argc, char* argv[]) {
     std::unique_ptr<Config> config = std::make_unique<Config>();
     bool has_broken_vulkan = false;
@@ -4455,6 +4495,8 @@ int main(int argc, char* argv[]) {
     }
 #endif
 
+    SetHighDPIAttributes();
+
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     // Disables the "?" button on all dialogs. Disabled by default on Qt6.
     QCoreApplication::setAttribute(Qt::AA_DisableWindowContextHelpButton);
@@ -4462,6 +4504,7 @@ int main(int argc, char* argv[]) {
 
     // Enables the core to make the qt created contexts current on std::threads
     QCoreApplication::setAttribute(Qt::AA_DontCheckOpenGLContextThreadAffinity);
+
     QApplication app(argc, argv);
 
 #ifdef _WIN32