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/puberty_simulator/src/lib.rs

@@ -431,7 +431,8 @@ impl ClapPlugin for PubertySimulator {
 
 impl Vst3Plugin for PubertySimulator {
     const VST3_CLASS_ID: [u8; 16] = *b"PubertySim..RvdH";
-    const VST3_CATEGORIES: &'static str = "Fx|Pitch Shift";
+    const VST3_SUBCATEGORIES: &'static [Vst3SubCategory] =
+        &[Vst3SubCategory::Fx, Vst3SubCategory::PitchShift];
 }
 
 nih_export_clap!(PubertySimulator);