Sort JSON output for CSS custom properties alphabetically

[web-padawan]

There is a small room for improvement after #111 has been merged: as of now, custom CSS properties are in the reverse order (compared to how they are annotated in JSDOc).

I would recommend to either keep the original order or sort alphabetically, as the issue says.

[runem]

Do you think all arrays should be sorted alphabetically (attributes, properties, events, slots and cssProperties) or only CSS custom properties? In that case I'll make sure to sort them all.