wp-bind improvements and negation in runtime

[luisherranz]

What

• I've added support for negations to the JavaScript runtime: data-wp-bind.checked="!state.checked".
• I've improved data-wp-bind to modify attributes on hydration (Preact doesn't modify them when using hydrate).
• I've added e2e tests for data-wp-bind, including one that uses "!state.checked".

Why

Because ! is easy enough to add, and it's very useful when combined with data-wp-show or data-wp-bind.hidden (if/else).

How

• For the negation, just check if the path starts with !.
• For the data-wp-bind, add a useEffect and change the DOM manually to reflect the vDOM (similar to data-wp-class).

Notes

1. While working on data-wp-bind.checked, I stumbled upon this weird thing: When you change the checked attribute of a node with React (reproduced here) or Preact (reproduced here), the browser doesn't update the checked attribute of the component. Everything seems to work because element.checked is correct and Dan says this is correct way of doing it, but at first it's pretty confusing 😅
2. I'll work on the server-side negation in another PR.

[SantosGuillamot]

Looks great to me! 🙂