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.
Substitue each Version.new and HeadVersion.new with Version.create
to unify Version and HeadVersion instantiation among core code.
Note that this does not relate to Mac::OS::Version class.
Dependency is another similar, related class and it's super confusing
to have some Requirements that are named *Dependency.
ClosesHomebrew/homebrew#38891.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
