By extending this class, a class can define its own `getLocation`
predicate without participating in the dispatch hierarchy of
`getLocation` as defined on `Element`. Classes wanting to override their
location previously had to define `getURL` or `hasLocationInfo` instead
and rely on these predicates not being defined on future versions of
`Element`.
This changes the test output because `VariableDeclarationGroup.toString`
changes to be the one inherited from VariableDeclarationEntry. This
should not affect the output as shown by any front end because
the string to be displayed to the user for a `$@` interpolation comes
from the following column instead.
