cocci: introduce rules to transform "refs" to pass ref store

cocci: introduce rules to transform "refs" to pass ref store

Most of the functions in "refs.h" have two flavors: one that accepts a
`struct ref_store`, and one that figures it out via `the_repository`.
As part of the libification efforts we want to get rid of the latter
variant and stop relying on `the_repository` altogether.

Introduce a set of Coccinelle rules that transform callers of the "refs"
interfaces to pass a `struct ref_store`. These rules are not yet applied
by this patch so that it can be reviewed standalone more easily. This
will be done in the next patch.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>