feature request: ApplicationCommands implementation in core module

[psygate]

Feature Description:

API components like ApplicationCommandData use Strings as ids, while Rest API components like ApplicationService#deleteGlobalApplicationCommand take Longs as IDs. The intention to have the ApplicationService properly typed and not just operate on raw data is visible in ApplicationService#createGlobalApplicationCommand(long applicationId, ApplicationCommandRequest request). This should be normalized and all ApplicationService methods should either use primitives with explicit casting mechanisms (IDs become Snowflakes and the dev explicitly casts to snowflakes), or all methods should use intermittent types like Snowflakes or directly take the existing ApplicationCommandData as an argument. Number 2 makes more sense, since you can only ever delete an existing command, but creates more interdependency with the Discord-JSON Subproject

Justification: It's not clear which parts of the API are supposed to fit together and work together when primitive types like Strings are used on the one side and the other sides requires explicitly casted types like longs or snowflakes.