* Add code action for filling type holes
* Incorporate hole name into action title
Useful if more than one hole appears on the same line. Not so useful
if both of these holes are just `_` rather than `_name` (or more than
one hole on the same line has the same `_name`): In which case perhaps
some numbers could be attached to the action titles, to distinguish
the holes. But I suspect that this would not be worth the effort.
* Add tests for fill-type-hole actions
* Disable two tests on GHC 8.4
These test hints about local bindings, whic GHC 8.4 does not provide.
* Replace compilerVersion with new MIN_GHC_API_VERSION macro