This PR enables scrolling horizontally in the tab bar.
Currently this requires holding down <kbd>Shift</kbd> for the scroll to
activate. We'll need to look into this.
Scrolling also currently works when there is a split in the editor, as
the non-split view goes down a different rendering path that does not
constrain the pane width, which breaks a number of things.
Release Notes:
- N/A
Marshall Bowers
e489e2e583