Replace VST3 category string with enum slice

I've been putting this off for a while, but now is finally the day. We
already did this for CLAP a while back. This is both simpler and less
error prone.

plugins/examples/sysex/src/lib.rs

@@ -102,7 +102,11 @@ impl ClapPlugin for SysEx {
 
 impl Vst3Plugin for SysEx {
     const VST3_CLASS_ID: [u8; 16] = *b"SysExCoolPluginn";
-    const VST3_CATEGORIES: &'static str = "Fx|Instrument|Tools";
+    const VST3_SUBCATEGORIES: &'static [Vst3SubCategory] = &[
+        Vst3SubCategory::Fx,
+        Vst3SubCategory::Instrument,
+        Vst3SubCategory::Tools,
+    ];
 }
 
 nih_export_clap!(SysEx);