Non-punning list and tuple syntax (-XListTuplePuns, -XNoListTuplePuns)

This ticket is to track the implementation of GHC Proposal #475 "Non-punning list and tuple syntax".

I intend to break the implementation into multiple parts, so here's a checklist for things that have been implemented and merged so far:

Export Unit, Solo, Tuple<n> from GHC.Tuple
Export CUnit, CSolo, CTuple<n> from GHC.Classes, GHC.Exts
Export Unit#, Solo#, Tuple<n>#, and Sum<n># from GHC.Exts
Export Tuple, TupleArgKind, Constraints, TupleArgKind#, Tuple#, and Sum# from GHC.Tuple
Export List from GHC.Types and GHC.List (02279a9c)
Create GHC.Prelude and re-export Unit, Solo, Tuple<n>, CUnit, CSolo, CTuple<n>, List.
Implement the ListTuplePuns extension to control parsing and pretty-printing.

The proposal also prescribes to remove the Solo pattern synonym in three releases. Since this is to be done later, it will be tracked in a separate ticket.

Edited Apr 07, 2022 by Vladislav Zavialov

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