Typechecker for pattern synonyms, called from tcTyClsInstDecls
ConLike is a type for constructor-like things: real data constructors and pattern synomys.
typecheck & instantiate pattern synonym patterns in patterns and expressions
Desugaring for PatSynDecl
Parser: pattern exports
Add pattern synonyms to md_decls
IfacePatSyn
Globalise wrapper ID
add bidirectional pattern synonym wrappers to keep_alive list