[Glimmer2] Move hash helper to use reference infra

[chadhietala]

This may or may not be correct. Was just looking at the {{if}}/{{unless}} helpers.

[chancancode]

I think we want to make a special kind of Reference for this to proxy .get to NamedArgs#get. That way, if you never call HashHelperReference#value directly, we won't have to re-ify that into a dictionary and pull from the other references in the hash.

i.e. Upstream = {{yield (hash a=... b=... c=... d=.. e=...}}, and downstream only uses {{hash.a}} in the template, all won't have to re-ify the other four references (and also make a dictionary/object to hold all of the references/values)

[chancancode]

🎉