#1424: Trial changing a small number of inner enums to classes/interfaces to better support custom values

This PR is a subset of the enum PR #931 and is designed as a low impact
trial run of the design and backwards compatibility to inform
subsequent development.

Additional plugin compatibility features may be available by setting
`settings.compatibility.enum-compatibility-mode` to `true` in
`bukkit.yml`.

By: DerFrZocker <derrieple@gmail.com>

paper-server/src/main/resources/configurations/bukkit.yml

@@ -25,6 +25,7 @@ settings:
     use-map-color-cache: true
     compatibility:
         allow-old-keys-in-registry: false
+        enum-compatibility-mode: false
 spawn-limits:
     monsters: 70
     animals: 10