feat(model): derive Default for ActionRow

[itohatweb]

Since action rows only contain a components vector deriving default should be no problem.

[vilgotf]

Unlikely for Discord to break this type's API (where default is impossible)

[zeylahellyer]

What's the motivation?

[itohatweb]

Mostly because of #1752
Thinking of whether doing

let components = ComponentsBuilder()::new()
    .action_row(ActionRow { components: Vec::new() })
    .build();

or just

let components = ComponentsBuilder()::new()
    .action_row(Default::default())
    .build();

Also as vilgotf has said it's unlikely that ActionRow will get any change which would cause us removing Default.

[zeylahellyer]

Why would one want an empty action row?

[itohatweb]

I saw quite a few use cases where people start with an empty action row and populated it later.

[zeylahellyer]

I'm not personally convinced from the examples provided that it's worth making this commitment. It feels like if one has a ComponentsBuilder then an action_row method should take a built action row, not an action row to be later modified; in other words, there would rather be an ActionRowBuilder that builds an action row and is then passed to ComponentsBuilder, removing the state of the empty action row in the context of builders.

[7596ff]

I'm also not in favor of this change. Going to give this a close.