Update the order entity label to "Order [order:number]"

The current label for placed orders is just the order number. This is a change from Commerce 1.x, where we included the word "Order" in the label, and I couldn't find any closed issues discussion the change.

It creates an inconsistent UX through the interface where you'd expect to see "Order 123" atop a view page or in a breadcrumb, and it led us to put the word "order" into various messages where it didn't need to be. That wasn't a terrible issue until we fixed the lack of a label callback for draft orders / carts.

The proposal in this ticket is to update the order entity label to "Order [order:number]" as it was in Commerce 1.x and to review any necessary interface text changes throughout the codebase.