Simon Peyton Jones authored Jan 18, 2021 and Marge Bot committed Jan 29, 2021

Provoked by #19074, this patch makes GHC.Core.PatSyn.PatSyn
immutable, by recording only the *Name* of the matcher and
builder rather than (as currently) the *Id*.

See Note [Keep Ids out of PatSyn] in GHC.Core.PatSyn.

Updates haddock submodule.