Implement replace_css_class action

[leonvogt]

This PR implements the replace_css_class action.

I ended up not using the suggested replace() function from the issue, because I didn't saw a way to use it with multiple classes.
The downside of my implementation is, it could change the order of the classes.
But I think that shouldn't be a big problem, since the order of the classes shouldn't matter.

closes #52

[marcoroth]

Hey @leonvogt, thanks for this pull request!

I'm wondering if we should just limit this action to one class in the from and to.

The classList.replace() function has some nuances which are currently not respected in this implementation. While in most cases the outcome is/should be the same, the classList.replace() only replaces the class when the element has the from class. Your implementation would add the to class in any case.

There might be an opportunity in TurboPower Rails to make it easier to use and to account for multiple classes. In that case the Rails helper could just return multiple <turbo-stream action="replace_css_class"></turbo-stream> tags in the same string. Or alternatively, we could provide another replace_css_classes that more or less does what you were doing here.

Technically it would be fine to implement it like you have it here, but since we are trying to stay as close as possible to the native web APIs I think we should change the replace_css_class to just take in one class.

[leonvogt]

Hey @marcoroth, thanks for the feedback!
I think your concerns are very reasonable. I didn't thought about the fact that the replace method only replaces the class if the element has the from class.
I've updated the PR to only replace one class at a time.

[marcoroth]

Thanks for updating the pull request, @leonvogt!