[Twig] Allow string[] for ComponentAttribute values

[kbond]

Q	A
Bug fix?	no
New feature?	yes
Issues	n/a
License	MIT

This allows the following:

{% set errors = false %}
{% set valid = true %}

<div{{ attributes.defaults({
    class: [
        'form-row',
        errors ? 'has-errors',
        valid ? 'is-valid',
    ],
}) }})

{# renders as: #}
<div class="form-row is-valid">

[kbond]

This normalization tracking is required because of how #1041 was implemented. (it first sets all passed values as attributes, then removes the ones that are defined)

[norkunas]

I'd use html_classes for this case :)

[kbond]

I'd use html_classes for this case :)

Forgot about that function! We can close this if others agree using that function is best.

[weaverryan]

Yup! I think the goal should be to make using html_classes() as easy as possible, and possibly document it, as this is a common need.