Allow choices to be specified for other application command option types

[dshepsis]

Application command options are documented here: https://discord.com/developers/docs/interactions/application-commands#application-command-object-application-command-option-structure

One of the fields for options is choices, which limits the permitted values shown to the user for the given option. Currently, this field can only be configured for STRING, INTEGER, and NUMBER option types. I suggest that choices be implemented for the USER, CHANNEL, ROLE, and MENTIONABLE option types.

The reason for this suggestion is that, currently, when using any of the latter option types, the user is shown a list of all possible options. This is often undesirable if a command is only intended to function with a specific set of options.

For example, consider a bot command which allows a user to assign themselves a role to change their role color. The server may have other roles related to permissions, which wouldn't be relevant to the command. If the command uses a ROLE-type option, those other roles would be included in the list alongside the color roles. As a workaround, the command could use the STRING option type and set the choices field to the list of color roles. However, one of the main benefits of the ROLE option type is that the roles displayed as options to the user have a text color corresponding to their role color. STRING option choices are always displayed in a normal black/white text color. I don't see any particular reason why we can't have the benefits of both role colors and a limited choices menu.

With respect to implementation, the choices field currently accepts an array of objects, each with a name and value field. name determines the text that appears in the suggested choices menu for the option. value determines the actual value for that option sent back to the bot. For example, for a STRING-type option, a choice could be shown to the user as "Foo" (name), but be sent to the bot as "Bar" (value). In the case of the USER, CHANNEL, ROLE, and MENTIONABLE option types,

The most obvious implementation would be for the corresponding id to be given in the value field, and the name field to give the name of that user/channel/role. Of course, the name should be determinable from the id, so I would additionally suggest that the name field be made optional. In the case of the STRING, INTEGER, and NUMBER option types, omitting the name of a choice would result in the value being shown to the user in the choice menu instead. In the case of the USER, CHANNEL, ROLE, and MENTIONABLE option types, omitting the name would result in the resolved name corresponding to the given id being shown to the user in the choice menu.