Remove "backpassing" and add "the `!` operator"

[ageron]

This interactive code example does not include backpassing, unless I'm mistaken. Instead, it uses the ! operator. I also reordered the syntax sugar list to match the order they appear in the example.

[ageron]

My understanding is that "backpassing" only refers to the <- syntax (as explained in roc-for-elm-programmers.md).

But perhaps using ! is also called "backpassing"? If so, then this should be explained in the interactive example, as well as in the tutorial.