Improves and enhances the reactive styling

[Lysander]

The description of the improved styling can be found in our documentation:

• General Function

• Avoid Flicker Effects

• removes addToClasses functions. Migration: Just rename all occurrences to className.

• substitutes the internal class name management with a MutableStateFlow based approach, where the former manages all different portions of the overall class names, so those can get merged appropriately and mounted only once into the tag's class attribute.

• add a new className-function variant: This generic function accepts some Flow[T], which is then be used by some lamba expression to generate the class names. Additionally the calles must also provide some initial T, which is used to create the   initial class names that gets set immediately to the DOM, without needing to wait for the flow's first value.

• add unit tests for new className-function

• add and adapt documentation

• updates Playwright to version 1.40.1

[Lysander]

Documentation is still missing, so I reset this do draft.

[jamowei]

This PR is api-breaking please provide a migration guide for the release notes (addToClasses -> className)