Rework precise capturing syntax

compiler/rustc_hir/src/hir.rs

@@ -463,6 +463,7 @@ pub enum TraitBoundModifier {
 pub enum GenericBound<'hir> {
     Trait(PolyTraitRef<'hir>, TraitBoundModifier),
     Outlives(&'hir Lifetime),
+    Use(&'hir [PreciseCapturingArg<'hir>], Span),
 }
 
 impl GenericBound<'_> {
@@ -477,6 +478,7 @@ impl GenericBound<'_> {
         match self {
             GenericBound::Trait(t, ..) => t.span,
             GenericBound::Outlives(l) => l.ident.span,
+            GenericBound::Use(_, span) => *span,
         }
     }
 }
@@ -2689,8 +2691,6 @@ pub struct OpaqueTy<'hir> {
     /// originating from a trait method. This makes it so that the opaque is
     /// lowered as an associated type.
     pub in_trait: bool,
-    /// List of arguments captured via `impl use<'a, P, ...> Trait` syntax.
-    pub precise_capturing_args: Option<(&'hir [PreciseCapturingArg<'hir>], Span)>,
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]