This PR makes clicking the label inside of a `ListHeader` with a
disclosure also toggle the disclosure.
Release Notes:
- Added support for clicking the "Online", "Offline", and "Requests"
headers in the contact list to toggle their expansion.
This PR renames the `IconElement` component to just `Icon`.
This better matches the rest of our components, as `IconElement` was the
only one using this naming convention.
The `Icon` enum has been renamed to `IconName` to free up the name.
I was trying to come up with a way that would allow rendering an
`Icon::Zed` directly (and thus make the `IconElement` a hidden part of
the API), but I couldn't come up with a way to do this cleanly.
Release Notes:
- N/A
