This PR removes the `ZedAssistant2` icon.
I went to use it as a placeholder icon, but noticed that the icon wasn't
loaded properly due to a name mismatch.
However, since we aren't using it anywhere I'm opting to remove it.
Release Notes:
- N/A
This PR adds a new `icons` crate and moves the `IconName` into it.
We have a number of crates that are taking a dependency on `ui` just so
they can talk about icons, which is not ideal.
Release Notes:
- N/A