Auto merge of #98120 - TaKO8Ki:box-diagnostic-metadata-field, r=estebank

[Experiment] Box `diagnostic_metadata` field

closes #97954

r? `@estebank`

Author: bors

Diff for: compiler/rustc_resolve/src/late.rs

@@ -544,7 +544,7 @@ struct LateResolutionVisitor<'a, 'b, 'ast> {
     current_trait_ref: Option<(Module<'a>, TraitRef)>,
 
     /// Fields used to add information to diagnostic errors.
-    diagnostic_metadata: DiagnosticMetadata<'ast>,
+    diagnostic_metadata: Box<DiagnosticMetadata<'ast>>,
 
     /// State used to know whether to ignore resolution errors for function bodies.
     ///
@@ -1157,7 +1157,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             label_ribs: Vec::new(),
             lifetime_ribs: Vec::new(),
             current_trait_ref: None,
-            diagnostic_metadata: DiagnosticMetadata::default(),
+            diagnostic_metadata: Box::new(DiagnosticMetadata::default()),
             // errors at module scope should always be reported
             in_func_body: false,
             lifetime_uses: Default::default(),