Introduce PTR-tagging for big constructor families
Currently only small constructor families come into the benefit of pointer tagging.
In big fams, 1 is the tag that says "I am evaluated". I suggest to do best-effort pointer tagging on big families too by this scheme:
Ptr-tag 1..6 for the first 6 constructors, 7 would signify "look into the info table and branch on that tag". In the info table the tags will then be 6..(familySize - 1).
I have an implementation which I'll submit to fabricator soon.
TODOs: update wiki pages.