This probably has to wait until 2.7.0 now and will require a bunch of
formula changes/deprecations but we should probably start moving in this
direction given we're not installing any of these on our CI any more.
The `cask` attribute doesn't make as much sense on Linux but can be
ignored there. The advantage of this change is that (like #4086) it
allows figuring out the relevant cask for a formulae requirement on a
Linux machine.
