[Twig][Live] null attribute values render without value (ie autofocus)

[kbond]

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

Ref: #220 (comment)

A null attribute value renders without the value:

{# templates/components/my_component.html.twig #}
<input{{ attributes}}/>

{# render component #}
{{ component('my_component', { type: 'text', value: '', autofocus: null }) }}

{# renders as: #}
<input type="text" value="" autofocus/>

TODO:

• null vs '' ([Twig][Live] add component attribute system/helper #220 (comment))
• attributes without a value like autofocus ([Twig][Live] add component attribute system/helper #220 (comment))
• LiveComponent dehydration/hydration issues (null values are lost during re-render) - solved in Send data back and forth as JSON #264

[kbond]

Pending a final review, I believe this ready to go.

I found a bug in the CI (build-packages.php wasn't called correctly). I fixed in this PR but can move to another if desired. Fixed in #267.

[weaverryan]

Thanks Kevin!