Attach command on Choice for translator

[Soheab]

Summary

This PR adds a command property to app_commands.Choice that can only be used to access the.. command inside the translator's translate method.

I wasn't sure on always attaching the command on the Choice since it doesn't store any state and is pretty lightweight.

Why?

Currently, there is no way to access the command if context.location is TranslationContextLocation.choice_name in app_commands.Translator.translate which is useful for implementations that store the strings per command name.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[Rapptz]

locale_str contains kwargs which allows you to specify as much extra information as possible when constructing it, so this should really not be necessary, especially since it kind of bloats up the model.