[WIP] Impl rewrite_result for ast nodes in types.rs

[ding-young]

Tracked by https://github.com/rust-lang/rustfmt/issues/6206

Description

• [ ] SegmentParam
• [ ] ast::AssocConstraint - will work on further pr with rewrite_generic_args
• [x] ast::AssocConstraintKind
• [ ] ast::WherePredicate - will work on further pr with rewrite_assign_rhs
• [x] ast::GenericArg
• [ ] ast::AnonConst - directly calls format_expr, so better delay until almost every ast node that corresponds to ExprKind has rewrite_result implementation
• [ ] ast::Lifetime - does it worth replacing at this point? it just wraps String with Some
• [x] ast::GenericBound
• [x] ast::GenericBounds
• [x] ast::GenericParam
• [ ] ast::PolyTraitRef
• [ ] ast::TraitRef - calls rewrite_path. will work on further pr for refactoring rewrite_path
• [x] ast:Ty

TODO