Rollup merge of #80538 - JulianKnodt:err_usize, r=lcnr

Add check for `[T;N]`/`usize` mismatch in astconv

Helps clarify the issue in #80506
by adding a specific check for mismatches between [T;N] and usize.

r? `@lcnr`

compiler/rustc_hir/src/hir.rs

@@ -290,6 +290,14 @@ impl GenericArg<'_> {
             GenericArg::Const(_) => "const",
         }
     }
+
+    pub fn to_ord(&self, feats: &rustc_feature::Features) -> ast::ParamKindOrd {
+        match self {
+            GenericArg::Lifetime(_) => ast::ParamKindOrd::Lifetime,
+            GenericArg::Type(_) => ast::ParamKindOrd::Type,
+            GenericArg::Const(_) => ast::ParamKindOrd::Const { unordered: feats.const_generics },
+        }
+    }
 }
 
 #[derive(Debug, HashStable_Generic)]