Add registrytest testplugin

[ImMorpheus]

Current output:

[Server thread/ERROR] [registrytest]: Registry minecraft:painting_variant is empty
[Server thread/ERROR] [registrytest]: Biomes.registry() does not exist
[Server thread/ERROR] [registrytest]: Registry minecraft:worldgen/configured_carver is empty
[Server thread/ERROR] [registrytest]: EntityCategories.registry() does not exist
[Server thread/ERROR] [registrytest]: Class ProcessorType in registry minecraft:worldgen/structure_processor is not annotated with CatalogedBy
[Server thread/ERROR] [registrytest]: PushReactions.registry() failed: null
[Server thread/ERROR] [registrytest]: StatisticCategories.registry() returned a different registry than the one specified in RegistryTypes
[Server thread/ERROR] [registrytest]: Registry minecraft:banner_pattern is empty
[Server thread/ERROR] [registrytest]: Class CommandRegistrarType in registry sponge:command_registrar_type is not annotated with CatalogedBy
[Server thread/ERROR] [registrytest]: Class Currency in registry sponge:currency is not annotated with CatalogedBy
[Server thread/ERROR] [registrytest]: DripstoneSegments.registry() does not exist
[Server thread/ERROR] [registrytest]: EquipmentGroups.HAND.find() is empty
[Server thread/ERROR] [registrytest]: EquipmentGroups.HUMANOID_ARMOR.find() is empty
[Server thread/ERROR] [registrytest]: Class ItemRarity in registry sponge:item_rarity is not annotated with CatalogedBy
[Server thread/ERROR] [registrytest]: Registry minecraft:jukebox_playable is empty
[Server thread/ERROR] [registrytest]: Class ValueParameter in registry sponge:value_parameter is not annotated with CatalogedBy
[Server thread/ERROR] [registrytest]: SculkSensorStates.registry() does not exist
[Server thread/ERROR] [registrytest]: ItemDisplayTypes.registry() returned a different registry than the one specified in RegistryTypes
[Server thread/ERROR] [registrytest]: Registry sponge:ticket_type is empty
[Server thread/ERROR] [registrytest]: TrialSpawnerStates.registry() failed: null
[Server thread/ERROR] [registrytest]: Tilts.registry() does not exist