Give options a designated initializer to make crossreferencing their usage easier (#905)

## Description of change
This always bothered me, you have a commandline arg and it's a massive
pain in the ass to work out where it's used because the flag never
really matches the enum name.

Array designated initializers are a C99 extension that clang+gcc both
support. I suspect msvc still blows up, but are people still using that?
I can change it to a std::invoke lambda instead.

Chose to drop the (unused?) option sorting func because, well, unused.

## Testing
Builds in CI, didn't do much more intense testing.

src/spice2x/launcher/options.h

@@ -325,6 +325,8 @@ namespace launcher {
             OBSWebSocketDebug,
             ScreenshotIncludeOverlay,
             ScreenshotSubscreens,
+
+            _Count,
         };
 
         enum class OptionsCategory {