commit-graph: stop using `the_hash_algo` via macros

commit-graph: stop using `the_hash_algo` via macros

We have two macros `GRAPH_DATA_WIDTH` and `GRAPH_MIN_SIZE` that compute
hash-dependent sizes. They do so by using the global `the_hash_algo`
variable though, which we want to get rid of over time.

Convert these macros into functions that accept the hash algorithm as
input parameter. Adapt callers accordingly.

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