Add a variant of `spawn` that returns the spawned entity's ID

[joseph-gio]

What problem does this solve or what need does it fill?

A very common pattern for spawning entities looks like this:

let id = commands
    .spawn((
        Transform::default(),
        GlobalTransform::default(),
    ))
    .id();

The .id() call makes rustfmt add an extra level of indentation, which makes the code worse.

What solution would you like?

Add a variant of spawn that returns the spawned entity's ID:

let id = commands.spawn_with_id((
    Transform::default(),
    GlobalTransform::default(),
));

What alternative(s) have you considered?

Instead of adding a new method, change spawn to return the entity's ID. I do not like this solution, since it would get in the way if you want to use EntityCommands.