Export list item types

[danyill]

Currently in the OscdFilteredList there are no types exported for the elements it encapsulates.

For instance I might want to type in my code:

• a list item
• a check box?
• the search field?

Should this component be exporting some types to assist users with this?

Normally when we didn't fully encapsulate I would do something like:

import type { ListItemBase } from '@material/mwc-list/mwc-list-item-base.js';

I am not very proficient with types so please let me know if this is not the correct way this should be done.