Add an ErrorGuaranteed to ast::TyKind::Err (attempt 2) This makes it more like `hir::TyKind::Err`, and avoids a `has_errors` assertion in `LoweringContext::lower_ty_direct`. r? ```@oli-obk```
MutVisitor::token_visiting_enabled
TokenStreamBuilder
String
ParseSess
Session
DiagnosticBuilder::emit
VariantData::Struct
recovered
ErrorGuaranteed
ast::LitKind::Err
token::LitKind::Err
EmitterWriter
HumanEmitter