GPUDevice: Add API version field

Also tie shader caches to API version and device LUID. That way we don't
have tons of cache files, and they're regenerated if the GPU/driver
changes.

src/core/host.h

@@ -20,7 +20,7 @@ class SettingsInterface;
 struct WindowInfo;
 enum class AudioBackend : u8;
 enum class AudioStretchMode : u8;
-enum class RenderAPI : u32;
+enum class RenderAPI : u8;
 class AudioStream;
 class CDImage;
 

src/core/settings.h

@@ -18,7 +18,7 @@
 #include <string_view>
 #include <vector>
 
-enum class RenderAPI : u32;
+enum class RenderAPI : u8;
 enum class MediaCaptureBackend : u8;
 
 struct SettingInfo