This was happening in the error recovery path when parsing accessors
on a pattern binding declaration that does not bind any variables, eg
let _: Int { 0 }
In invalid code a decl may end up with an opened archetype type that the
mangler doesn't expect. We still want to be able to generate a USR for these
decls so that we can index and rename their occurences successfully. To allow
this, this patch calls mapTypeOutOfContext on primary or opened archetype types
prior to mangling.
Resolves rdar://problem/54310026
Fixes a crash for SourceEntityWalker which assumed that a non-implicit TupleExpr has source locations for its name elements.
Fixes SR-6517, rdar://35830880