UP-TO-DATE checking for npm based step config

[simschla]

[DRAFT!] This PR introduces correct UP-TO-DATE checking for the npm based steps.

As discussed in #2140 I've tried both ways: Using (1) the current "serialization-as-equality-hack" or (2) implementing FormatterStep directly. After playing around, I think approach (2) leads to a simpler and clearer implementation.

So in this PR, I'd like to discuss this second approach based on the changed implementation of the EslintFormatterStep before I go all the way and change also TsFmt and Prettier.