configuration: Expose separate swap present modes

Previously, yuzu would try and guess which vsync mode to use given
different scenarios, but apparently we didn't always get it right. This
exposes the separate modes in a drop-down the user can select.

If a mode isn't available in Vulkan, it defaults to FIFO.

src/yuzu/bootmanager.cpp

@@ -154,7 +154,18 @@ public:
 
         // disable vsync for any shared contexts
         auto format = share_context->format();
-        format.setSwapInterval(main_surface ? Settings::values.use_vsync.GetValue() : 0);
+        const int swap_interval = [&]() {
+            switch (Settings::values.vsync_mode.GetValue()) {
+            case Settings::VSyncMode::Immediate:
+                return 0;
+            case Settings::VSyncMode::FIFO:
+                return 1;
+            case Settings::VSyncMode::Mailbox:
+                return 2;
+            }
+        }();
+
+        format.setSwapInterval(main_surface ? swap_interval : 0);
 
         context = std::make_unique<QOpenGLContext>();
         context->setShareContext(share_context);