Add FrozenDictionary/Set#77799

Merged

stephentoub merged 3 commits intodotnet:mainfrom

stephentoub:frozencollections

Nov 4, 2022

Commits on Nov 2, 2022

Import original frozen collections source with updates to successfully compile

stephentoub
and
Martin Taillefer
committed
Overhaul frozen collections (API, implementation, tests)
stephentoub
committed

Commits on Nov 3, 2022

Address PR feedback
stephentoub
committed