This commit gets rid of contain-it-all structs and instead opt for
interface union types containing underlying concrete types with no
overloading.
The code is much more verbose by doing this, but the API is much nicer
to use. The only disadvantage in that regard is the interface assertion
being too verbose and risky for users at times.
- Moved gateway.InteractionCreateData to discord.Interaction, now
gateway.InteractionCreateData is a struct that wraps
discord.Interaction.
- Split InteractionData into CommandInteractionData and
ComponentInteractionData.
- Renamed ButtonInteraction to ComponentInteraction.
- Updated api.CommandCreateData to add new fields.
- Update Component types' Type() methods to pointer receivers.
