Macro for spawning related entities can't be used with `SpawnableList`

[Shatur]

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

The children! macro is convenient, but it can’t be used with SpawnableLists. So if I need to use SpawnWith or SpawnIter, I have to fall back to Children::spawn, which isn’t very ergonomic.\

This design affects other crates too. For example, in BEI, the only way to represent presets is by using SpawnableList - and those can't be used with the related macro either:

  Bindings::spawn((Spawn(Binding::mouse_motion()), Axial::right_stick()))

What solution would you like?

The perfect solution would be to either adjust the macro or somehow change the design to avoid requiring the use of Spawn for RelationshipTarget::spawn.