GameRuleRegistry#register Shouldn't Take an Identifier

[Haven-King]

Identifiers must follow snake case, while vanilla gamerules use camelcase. This means custom gamerules can't follow vanilla conventions.

Can be worked around by calling GameRulesAccessor#invokeRegister manually, though that's not intuitive, and a merged version would ideally not require it.

[i509VCB]

Hmm, I could just let people pass a string through. And the game does crash if you register a rule with an existing rule key.