Unify git ref to sha lookups #16411
Description
example: #16400
... you can find ... code (git ref -> sha lookup) all over different places and we should unify them ...
As lunny worried utils is becoming a bit of a catch-all package. Not necessarily this PR but I wonder if we these would be better in a git package
cc @zeripath
note: "..Now a branch named deadbeef will override the sha deadbeef. I'm not sure if that's completely intentional, it may be best to provide some marker or mechanism to force sha over branches/tags.."