rustc: Harmonize DefKind and DefPathData

`DefPathData::(ClosureExpr,ImplTrait)` are renamed to match `DefKind::(Closure,OpaqueTy)`.

`DefPathData::ImplTraitAssocTy` is replaced with `DefPathData::TypeNS(kw::Empty)` because both correspond to `DefKind::AssocTy`.
It's possible that introducing `(DefKind,DefPathData)::AssocOpaqueTy` could be a better solution, but that would be a much more invasive change.

Const generic parameters introduced for effects are moved from `DefPathData::TypeNS` to `DefPathData::ValueNS`, because constants are values.

`DefPathData` is no longer passed to `create_def` functions to avoid redundancy.

compiler/rustc_ast_lowering/src/expr.rs

@@ -13,10 +13,9 @@ use rustc_ast::*;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::definitions::DefPathData;
 use rustc_session::errors::report_lit_error;
 use rustc_span::source_map::{respan, Spanned};
-use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
 use rustc_span::{DesugaringKind, Span};
 use thin_vec::{thin_vec, ThinVec};
@@ -376,7 +375,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 self.create_def(
                     parent_def_id.def_id,
                     node_id,
-                    DefPathData::AnonConst,
+                    kw::Empty,
                     DefKind::AnonConst,
                     f.span,
                 );