Use native setters in documentation examples

[allthesignals]

I think we should use native setter syntax in documentation examples. Is there a reason we should use .set? Backwards compatibility?

[Turbo87]

@allthesignals I don't think that this actually works properly. It works fine if you set these values before rendering a component, but setting it again afterwards won't invalidate the render, so AFAIK for now we still need the set() calls on the test context object.