Continuing from #13597, this PR refactors platform controls to extract a
generic set of platform controls that can be used for any platform that
does not define it's own/we don't use the system ones.
In the future, these controls will likely be used as a fallback on
windows as well when the windows icon font isn't available.
Release Notes:
- Added updated window controls on Linux
This PR extracts a singular title bar (`title_bar::TitleBar`) from
`ui::TitleBar` and
`collab_ui::collab_titlebar_item::CollabTitlebarItem`.
This is a first step towards organizing title bar things into one place,
and standardizing platform titlebar/window control implementations.
Release Notes:
- N/A