NutrientMainToolbarContent

What NutrientMainToolbar's slots hold by default, as one piece of content: the coordinator's title, then its items taking the width that is left (NutrientToolbarScope.weight) — so trailing items pin to the far edge of a full-bleed bar while a floating one stays as wide as its icons.

For a host on the content overload that wants the SDK bar plus something of its own.