CatalogType parser not working with all catalog types

[dualspiral]

Currently, the CatalogedTypeCommandElement tries to make a match with the ID of the catalogued type (using .getId()) as seen here in getChoices(CommandSource) in the GenericArguments class.

In the case of

GenericArguments.onlyOne(GenericArguments.catalogedElement(Text.of(difficulty), CatalogTypes.DIFFICULTY))

rather than expecting the names "EASY", "PEACEFUL" etc., it at first seems like it's actually expecting options.difficulty.easy, options.difficulty.peaceful, etc.

However, when control then passes to getValue(String), here we find that Sponge.getGame().getRegistry().getType(this.catalogType, choice); fails to find anything, because choice here is not expecting options.difficulty.easy, but EASY, so no match can ever be made.

Using the latest SpongeVanilla, where the last argument of the command is the difficulty, I find this happens, first for normal, then for options.difficulty.normal:

[18:12:30 INFO] [nucleus]: Server ran the command: /world create test overworld flat survival normal
[18:12:30 INFO]: No values matching pattern 'normal' present for difficulty!
create test overworld flat survival normal
                                    ^
[18:12:30 INFO]: Usage: /world setdifficulty|teleport|setgamemode|list|delete|setspawn|spawn|load|create
> world create test overworld flat survival options.difficulty.normal
[18:12:32 INFO] [nucleus]: Server ran the command: /world create test overworld flat survival options.difficulty.normal
[18:12:32 INFO]: Error occurred while executing command: Invalid input options.difficulty.normal was found
[18:12:32 ERROR] [Sponge]: Error occurred while executing command 'world create test overworld flat survival options.difficulty.normal' for source DedicatedServer: Invalid input options.difficulty.normal was found
java.lang.IllegalArgumentException: Invalid input options.difficulty.normal was found
        at org.spongepowered.api.command.args.GenericArguments$CatalogedTypeCommandElement.getValue(GenericArguments.java:1340) ~[GenericArguments$CatalogedTypeCommandElement.class:1.8.9-4.1.0-BETA-314]
        at org.spongepowered.api.command.args.PatternMatchingCommandElement.parseValue(PatternMatchingCommandElement.java:59) ~[PatternMatchingCommandElement.class:1.8.9-4.1.0-BETA-314]
        at org.spongepowered.api.command.args.CommandElement.parse(CommandElement.java:83) ~[CommandElement.class:1.8.9-4.1.0-BETA-314]

[ST-DDT]

Related: Broken CatalogTypes @ SpongeCommon #739

Excerpt from test plugin's error log (line 307f):

[ERROR]: Failed to obtain instance for Difficulty with id options.difficulty.normal
[ERROR]: Failed to obtain instance for Difficulty with id options.difficulty.hard
[ERROR]: Failed to obtain instance for Difficulty with id options.difficulty.easy
[ERROR]: Failed to obtain instance for Difficulty with id options.difficulty.peaceful