[!!!][TASK] Clean up placeholder on textfield and text area VHs
The form.textfield VH had a placeholder attribute as argument to the
render() method; the form.textarea VH did not support placeholder at all.
With this change the placeholder is available on both VHs but registered
as tag attribute.
If you extended TextfieldViewHelper::render() make sure to remove the
$placeholder argument, otherwise you will see
Argument "placeholder" has already been defined, thus it should not
be defined again.
errors from Fluid.