Support for binding class attribute to a string signal

[mshabarov]

A follow-up enhancement for #22670 (comment).

To add a support for element.bindAttribute("class", classListSignal):

• it overrides the possibly existing bindings between class names and boolean signals
• it removes the binding if classListSignal is null
• ClassList.bind(String, Signal<Boolean>) throws an exception if it sees that a "class"-to-signal binding already exists.

See:

• prototype for bind a string signal to class attribute.
• bind boolean signal to a class name

[Legioth]

What's the use case? In what kind of scenario would I want to have the class names as the value of a signal instead of having a boolean signal for each class name?