Rename the ConstS::val field as kind.

And likewise for the `Const::val` method.

Because its type is called `ConstKind`. Also `val` is a confusing name
because `ConstKind` is an enum with seven variants, one of which is
called `Value`. Also, this gives consistency with `TyS` and `PredicateS`
which have `kind` fields.

The commit also renames a few `Const` variables from `val` to `c`, to
avoid confusion with the `ConstKind::Value` variant.

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -353,7 +353,8 @@ where
 
     // Check the qualifs of the value of `const` items.
     if let Some(ct) = constant.literal.const_for_ty() {
-        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs: _, promoted }) = ct.val() {
+        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs: _, promoted }) = ct.kind()
+        {
             // Use qualifs of the type for the promoted. Promoteds in MIR body should be possible
             // only for `NeedsNonConstDrop` with precise drop checking. This is the only const
             // check performed after the promotion. Verify that with an assertion.

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -842,7 +842,7 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
                     literal: tcx
                         .mk_const(ty::ConstS {
                             ty,
-                            val: ty::ConstKind::Unevaluated(ty::Unevaluated {
+                            kind: ty::ConstKind::Unevaluated(ty::Unevaluated {
                                 def,
                                 substs: InternalSubsts::for_item(tcx, def.did, |param, _| {
                                     if let ty::GenericParamDefKind::Lifetime = param.kind {