Previously the exclusive fullscreen option in the settings screen was
guarded by a compile-time #ifdef VK_EXT_full_screen_exclusive, which is
always true on Windows. It now uses a runtime fullScreenExclusiveSupported
cap derived from whether the extension is actually enabled by the driver.
Switching between borderless and exclusive fullscreen currently requires a
restart. This is because once DWM has claimed the window (any frames
presented), ALLOWED_EXT cannot re-engage exclusive mode on an existing
swapchain. A new process gets a fresh HWND that DWM has not claimed yet,
so ALLOWED_EXT works correctly at startup.
The proper fix is to use VK_FULL_SCREEN_EXCLUSIVE_APPLICATION_CONTROLLED_EXT
with vkAcquireFullScreenExclusiveModeEXT/vkReleaseFullScreenExclusiveModeEXT
to explicitly negotiate exclusive mode with DWM mid-session without needing
a restart. To be done in a follow-up.